diff --git a/assets/webui/ofdgo.css b/assets/webui/ofdgo.css
index 313329f..5952d93 100644
--- a/assets/webui/ofdgo.css
+++ b/assets/webui/ofdgo.css
@@ -1655,6 +1655,7 @@ button.outline-link:hover {
 .edit-handle {
 	display: none;
 	position: absolute;
+	z-index: 1;
 	width: calc(9px / var(--surface-scale));
 	height: calc(9px / var(--surface-scale));
 	border: calc(1px / var(--surface-scale)) solid var(--accent);
diff --git a/assets/webui/ofdgo.js b/assets/webui/ofdgo.js
index 513ac66..b0da31f 100644
--- a/assets/webui/ofdgo.js
+++ b/assets/webui/ofdgo.js
@@ -433,6 +433,7 @@ const canvasEditor = new CanvasEditor(el.viewerPanel, {
 	onDrawText: beginCanvasText,
 	onDrawAnnotation: placeAnnotation,
 	onDrawInk: (index, points, style, pressure) => changeDocument("ofdgoInsertInk", null, index, JSON.stringify(points), style.lineWidth, pressure, style.strokeColor),
+	onPreviewText: (item, value, font, size) => callWASM("ofdgoPreviewText", item.index, item.id, value, font || null, size),
 	onCommitText: (item, value, fontData, color = null) => item.draft
 		? changeDocument("ofdgoInsertText", null, item.index, value, fontData || item.fontData, item.x, item.y, item.size, item.color, item.width, item.wrap, item.align, item.paragraphHeight, item.letterSpacing, ...textIndents(item))
 		: changeDocument("ofdgoUpdateText", item, value, fontData || null, item.size, color),
@@ -1637,7 +1638,7 @@ async function editCanvasObject(item) {
 		return;
 	}
 	if (item.type === "TextObject") {
-		if (!confirmTextReflow(item)) return;
+		if (!canEditObject(item, "textContent")) return;
 	} else if (!canEditObject(item, item.type === "ImageObject" ? "replaceImage" : "update")) return;
 	if (item.type === "PathObject") {
 		el.shapeWidth.focus();
@@ -1652,8 +1653,9 @@ async function editCanvasObject(item) {
 		const data = await callWASM("ofdgoEditorFont", item.font);
 		const face = new FontFace(`ofdgo-edit-${item.font}`, data.bytes);
 		await face.load();
+		const source = canEditObject(item, "layoutKnown") ? null : await callWASM("ofdgoPreviewText", item.index, item.id, item.text);
 		if (openSeq === state.openSeq && item.node.isConnected) {
-			canvasEditor.editText(item, face);
+			canvasEditor.editText(item, face, source);
 		}
 	} catch (err) {
 		if (openSeq === state.openSeq) {
@@ -1828,7 +1830,7 @@ async function beginCanvasText(index, box, surface, page) {
 function editorFonts(item) {
 	const fonts = fontManager.editorFonts();
 	if (item) {
-		fonts.unshift({ id: `embedded:${item.font}`, name: item.fontName || item.font, embedded: true, disabled: !canEditObject(item, "update") });
+		fonts.unshift({ id: `embedded:${item.font}`, name: item.fontName || item.font, embedded: true, disabled: !canEditObject(item, "textContent") });
 	}
 	return fonts;
 }
@@ -2712,7 +2714,7 @@ async function loadWASM() {
 				if (data.ok) {
 					request.resolve(data.data);
 				} else {
-					const err = new Error(missingGlyphMessage(data.missingGlyphs) || data.error);
+					const err = new Error(missingGlyphMessage(data.missingGlyphs) || (data.reasonCode === "layoutRequired" ? "请先设置段落排版，再跨段或换行修改" : data.error));
 					if (data.canceled) {
 						err.name = "AbortError";
 					}
@@ -4710,7 +4712,7 @@ async function selectSearchMatch(index) {
 	if (state.editing) {
 		const node = [...pageShell(match.page).querySelectorAll(".edit-object")].find(node => canvasEditor.nodes.get(node)?.id === match.id);
 		const item = node && canvasEditor.nodes.get(node);
-		if (item?.type === "TextObject" && canEditObject(item, "update")) {
+		if (item?.type === "TextObject") {
 			state.selectObjects = true;
 			setPan(false);
 			canvasEditor.setTool("");
@@ -6036,7 +6038,7 @@ function updateObjectControls(item, reset = false) {
 	el.resetCropButton.disabled = canEditObject(item, "resetCrop") ? disabled : el.cropImageButton.disabled || !cropping && (item.scoped ? !item.cropped : !item.imageBounds || ["x", "y", "width", "height"].every(key => Math.abs(item[key] - item.imageBounds[key]) < 1e-9));
 	el.objectDistribute.disabled = el.objectAlign.disabled || !item.items || item.items.length < 3;
 	el.editObjectButton.disabled = disabled || Boolean(item.items) || !canEditObject(item, "enter") && (item.type === "PathObject"
-		|| !canEditObject(item, item.type === "TextObject" ? "reflow" : item.type === "ImageObject" ? "replaceImage" : "update"));
+		|| !canEditObject(item, item.type === "TextObject" ? "textContent" : item.type === "ImageObject" ? "replaceImage" : "update"));
 	el.editObjectButton.textContent = canEditObject(item, "enter") ? "进入" : item?.type === "ImageObject" ? "替换" : "修改";
 	el.editObjectButton.title = canEditObject(item, "enter") ? item?.type === "Annotation" ? "进入注解" : "进入组合" : item?.type === "ImageObject" ? "替换图片" : item?.type === "Annotation" ? "修改注解" : "修改对象";
 	el.editObjectButton.setAttribute("aria-label", el.editObjectButton.title);
diff --git a/assets/webui/ofdgo_edit.js b/assets/webui/ofdgo_edit.js
index 26e9e4a..42d9697 100644
--- a/assets/webui/ofdgo_edit.js
+++ b/assets/webui/ofdgo_edit.js
@@ -11,6 +11,31 @@ export function editTextValue(input) {
 	return text;
 }
 
+function editTextSelection(input, saved) {
+	const selection = document.getSelection();
+	const points = saved ? [[saved.startContainer, saved.startOffset], [saved.endContainer, saved.endOffset]]
+		: selection?.rangeCount ? [[selection.anchorNode, selection.anchorOffset], [selection.focusNode, selection.focusOffset]] : null;
+	if (!points || points.some(([node]) => !input.contains(node))) return null;
+	return points.map(([node, position]) => {
+		const range = document.createRange();
+		range.selectNodeContents(input);
+		range.setEnd(node, position);
+		return editTextValue(range.cloneContents()).length;
+	});
+}
+
+function restoreTextSelection(positions, caret, saved) {
+	if (!caret || !positions.length) return;
+	const endpoints = caret.map(point => {
+		const entry = positions.find(entry => entry.end >= point) || positions.at(-1);
+		return [entry.node, Math.max(0, Math.min(point - entry.start, entry.node.length))];
+	});
+	if (saved) {
+		saved.setStart(...endpoints[0]);
+		saved.setEnd(...endpoints[1]);
+	} else document.getSelection().setBaseAndExtent(...endpoints[0], ...endpoints[1]);
+}
+
 export function pagePoint(x, y, rect, page, rotation) {
 	const u = (x - rect.left) / rect.width;
 	const v = (y - rect.top) / rect.height;
@@ -1145,7 +1170,7 @@ export class CanvasEditor {
 		}
 	}
 
-	editText(item, face) {
+	editText(item, face, source = null) {
 		this.cancel();
 		this.closeText();
 		this.select(item);
@@ -1178,17 +1203,28 @@ export class CanvasEditor {
 			letterSpacing: `${(item.letterSpacing || 0) * PX_PER_MM}px`,
 			textIndent: `${(item.firstLineIndent || 0) * PX_PER_MM}px`,
 		});
-		this.input = { input, item, face, fontChoice: item.fontChoice };
+		this.input = { input, item, face, source: Boolean(source), fontChoice: item.fontChoice };
 		const editing = this.input;
+		if (source) editing.history = { entries: [{ value: item.text }], index: 0 };
 		item.artwork?.classList.add("edit-text-source");
 		item.node.classList.add("edit-text-source");
 		item.surface.append(input);
-		input.addEventListener("input", () => this.options.onTextChange());
-		input.addEventListener("compositionstart", () => { editing.composing = true; });
+		if (source) this.paintSourceText(source);
+		input.addEventListener("input", () => {
+			this.recordSourceText();
+			this.options.onTextChange();
+			this.previewSourceText();
+		});
+		input.addEventListener("compositionstart", () => {
+			this.rememberSourceSelection();
+			editing.composing = true;
+		});
 		input.addEventListener("compositionend", () => {
 			editing.composing = false;
+			this.recordSourceText();
 			Promise.resolve().then(() => {
 				if (this.input === editing && editing.commitAfterComposition) this.commitText();
+				else this.previewSourceText();
 			});
 		});
 		input.addEventListener("paste", event => {
@@ -1196,6 +1232,12 @@ export class CanvasEditor {
 			document.execCommand("insertText", false, event.clipboardData.getData("text/plain"));
 		});
 		input.addEventListener("beforeinput", event => {
+			if (editing.source && (event.inputType === "historyUndo" || event.inputType === "historyRedo")) {
+				event.preventDefault();
+				this.restoreSourceText(event.inputType === "historyUndo" ? -1 : 1);
+				return;
+			}
+			this.rememberSourceSelection();
 			if (event.inputType.startsWith("format")) event.preventDefault();
 			if (event.inputType === "insertLineBreak") {
 				event.preventDefault();
@@ -1221,7 +1263,10 @@ export class CanvasEditor {
 			if (event.isComposing || editing.composing || editing.saving) {
 				return;
 			}
-			if (event.key === "Escape") {
+			if (editing.source && (event.ctrlKey || event.metaKey) && !event.altKey && ["z", "y"].includes(event.key.toLowerCase())) {
+				event.preventDefault();
+				this.restoreSourceText(event.key.toLowerCase() === "y" || event.shiftKey ? 1 : -1);
+			} else if (event.key === "Escape") {
 				event.preventDefault();
 				this.closeText();
 				this.focus();
@@ -1234,6 +1279,107 @@ export class CanvasEditor {
 		if (!item.draft) document.getSelection().selectAllChildren(input);
 	}
 
+	rememberSourceSelection() {
+		const editing = this.input;
+		if (editing?.history && !editing.composing) editing.history.entries[editing.history.index].caret = editTextSelection(editing.input);
+	}
+
+	recordSourceText() {
+		const editing = this.input;
+		if (!editing?.history || editing.composing) return;
+		const { history, input } = editing, value = editTextValue(input);
+		if (history.entries[history.index].value === value) return;
+		history.entries.splice(++history.index, Infinity, { value, caret: editTextSelection(input) });
+	}
+
+	restoreSourceText(direction) {
+		const editing = this.input, history = editing?.history;
+		if (!history || editing.composing || editing.saving) return;
+		const index = history.index + direction;
+		if (index < 0 || index >= history.entries.length) return;
+		history.index = index;
+		const entry = history.entries[index], fragment = document.createDocumentFragment(), positions = [];
+		let position = 0;
+		for (const text of entry.value.split("\n")) {
+			const paragraph = document.createElement("div");
+			const node = document.createTextNode(text);
+			paragraph.append(node);
+			positions.push({ node, start: position, end: position + text.length });
+			if (!text) paragraph.append(document.createElement("br"));
+			fragment.append(paragraph);
+			position += text.length + 1;
+		}
+		editing.input.replaceChildren(fragment);
+		restoreTextSelection(positions, entry.caret);
+		this.options.onTextChange();
+		this.previewSourceText();
+	}
+
+	async previewSourceText() {
+		const editing = this.input;
+		if (!editing?.source || editing.composing || editing.saving) return;
+		const value = editTextValue(editing.input), font = editing.fontData, size = editing.style?.size || editing.item.size;
+		const current = () => this.input === editing && !editing.composing && !editing.saving && editing.fontData === font
+			&& (editing.style?.size || editing.item.size) === size && editTextValue(editing.input) === value;
+		try {
+			const source = await this.options.onPreviewText(editing.item, value, font, size);
+			if (!current()) return;
+			editing.input.removeAttribute("aria-invalid");
+			editing.input.removeAttribute("title");
+			this.paintSourceText(source);
+		} catch (err) {
+			if (!current()) return;
+			editing.input.setAttribute("aria-invalid", "true");
+			editing.input.title = err.message;
+		}
+	}
+
+	paintSourceText(source) {
+		const editing = this.input, { input, item, face } = editing;
+		const caret = editTextSelection(input, editing.range);
+		const size = (editing.style?.size || item.size) * PX_PER_MM;
+		const context = document.createElement("canvas").getContext("2d");
+		context.font = `${source.italic ? "italic" : "normal"} ${source.weight || 400} ${size}px "${face.family}"`;
+		const metrics = context.measureText("Mg"), baseline = (size + metrics.fontBoundingBoxAscent - metrics.fontBoundingBoxDescent) / 2;
+		Object.assign(input.style, { lineHeight: `${size}px`, fontWeight: String(source.weight || 400), fontStyle: source.italic ? "italic" : "normal" });
+		const fragment = document.createDocumentFragment(), positions = [];
+		let line, lineIndex = -1, naturalX = 0, position = 0, width = 0, height = 0;
+		for (const run of source.runs) {
+			if (!line || run.line) {
+				if (line) position++;
+				line = document.createElement("div");
+				fragment.append(line);
+				lineIndex++;
+				naturalX = 0;
+			}
+			let x = run.x * PX_PER_MM, y = run.y * PX_PER_MM, index = 0;
+			for (const char of run.text) {
+				const span = document.createElement("span"), node = document.createTextNode(char);
+				span.append(node);
+				Object.assign(span.style, { display: "inline-block", opacity: String((item.alpha ?? 255) / 255), transformOrigin: "left top", transform: `translate(${x - naturalX}px,${y - baseline - lineIndex * size}px) scaleX(${source.scale})` });
+				line.append(span);
+				positions.push({ node, start: position, end: position + char.length });
+				position += char.length;
+				const advance = context.measureText(char).width;
+				width = Math.max(width, x + advance * source.scale);
+				height = Math.max(height, y + size - baseline);
+				naturalX += advance;
+				x += run.dx?.length ? run.dx[Math.min(index, run.dx.length - 1)] * PX_PER_MM : run.dy?.length ? 0 : advance * source.scale;
+				y += run.dy?.length ? run.dy[Math.min(index, run.dy.length - 1)] * PX_PER_MM : 0;
+				index++;
+			}
+			if (!line.hasChildNodes()) {
+				const node = document.createTextNode("");
+				line.append(node, document.createElement("br"));
+				positions.push({ node, start: position, end: position });
+			}
+		}
+		input.replaceChildren(fragment);
+		input.style.width = `${Math.max(parseFloat(input.style.width), width + 4)}px`;
+		input.style.minHeight = `${Math.max(parseFloat(input.style.minHeight), height + 4)}px`;
+		restoreTextSelection(positions, caret, editing.range);
+	}
+
 	setTextFont(face, data) {
 		const editing = this.input;
 		document.fonts.add(face);
@@ -1243,6 +1389,7 @@ export class CanvasEditor {
 		editing.input.style.fontFamily = `"${face.family}"`;
 		this.options.onTextChange();
 		editing.input.focus({ preventScroll: true });
+		this.previewSourceText();
 	}
 
 	setTextStyle(values) {
@@ -1254,6 +1401,7 @@ export class CanvasEditor {
 		editing.input.style.fontSize = `${item.size * PX_PER_MM}px`;
 		editing.input.style.color = item.color;
 		this.options.onTextChange();
+		if ("size" in values) this.previewSourceText();
 	}
 
 	textChanged() {
diff --git a/internal/webui/wasm.go b/internal/webui/wasm.go
index 5cee3e5..2e0617c 100644
--- a/internal/webui/wasm.go
+++ b/internal/webui/wasm.go
@@ -134,6 +134,7 @@ func RunWASM() {
 	registerAsyncCallback("ofdgoImportPages", importPages)
 	registerCallback("ofdgoInsertText", insertText)
 	registerCallback("ofdgoUpdateText", updateText)
+	registerCallback("ofdgoPreviewText", previewText)
 	registerCallback("ofdgoStyleText", styleText)
 	registerCallback("ofdgoCheckTextFont", checkTextFont)
 	registerCallback("ofdgoInsertImage", insertImage)
@@ -1615,6 +1616,7 @@ func pasteEditorSelection(page int, clipboard *editorClipboard, dx, dy float64)
 func editorCapabilities(capability ofdgo.ObjectCapabilities, kind string) map[string]any {
 	result := map[string]any{"update": capability.Update, "paint": capability.Paint, "replaceFont": capability.ReplaceFont, "reflow": capability.Reflow, "layoutKnown": capability.LayoutKnown, "transform": capability.Transform, "arrange": capability.Arrange, "copy": capability.Copy, "delete": capability.Delete, "order": capability.Order, "reason": capability.Reason, "reasonCode": string(capability.ReasonCode),
 		"replaceImage": capability.ReplaceImage, "cropImage": capability.CropImage, "fitImage": capability.FitImage, "resetCrop": capability.ResetCrop, "ungroup": capability.Ungroup, "stretch": capability.Stretch, "enter": capability.Transform && (kind == "CompositeObject" || kind == "CompositeGraphicUnit")}
+	result["textContent"] = capability.TextContent
 	if missing := capability.MissingGlyphs; missing != nil {
 		result["missingGlyphs"] = map[string]any{"fontID": missing.FontID, "characters": missing.Characters}
 	}
@@ -1985,20 +1987,114 @@ func changeCompositeText(page int, path ofdgo.ObjectPath, indexes []int, operati
 	return currentEditor.StyleCompositeText(page, path, indexes, style)
 }
 
-// editorFont 读取对象实际使用的内嵌字体，供画布输入使用
+// editorFont 读取对象编辑使用的字体，匹配的外部字体不嵌入文档
 // 入参: args 字体资源标识
 // 返回: any 字体数据, error 错误信息
 func editorFont(args []js.Value) (any, error) {
 	if currentEditor == nil {
 		return nil, fmt.Errorf("no document is being edited")
 	}
-	data, err := currentSession.Reader.FontData(args[0].String())
+	data, err := currentEditor.FontData(args[0].String())
 	if err != nil {
 		return nil, err
 	}
 	return successResult(map[string]any{"bytes": bytesToJS(data)}), nil
 }
 
+// previewText 生成保留原定位的输入预览，不修改文档或历史
+// 入参: args 页码、对象路径、新文字、可选字体数据和字号
+// 返回: any 定位段及字体样式, error 错误信息
+func previewText(args []js.Value) (any, error) {
+	if currentEditor == nil {
+		return nil, fmt.Errorf("no document is being edited")
+	}
+	page, key := args[0].Int(), args[1].String()
+	var object ofdgo.GraphicObject
+	if separator := strings.LastIndex(key, "/"); separator >= 0 {
+		path, err := compositePath(key[:separator])
+		if err != nil {
+			return nil, err
+		}
+		member, err := strconv.Atoi(key[separator+1:])
+		if err != nil {
+			return nil, err
+		}
+		members, err := currentEditor.CompositeObjectsAt(page, path, []int{member})
+		if err != nil {
+			return nil, err
+		}
+		object = members[0].Object
+	} else {
+		var err error
+		object, err = currentEditor.Object(page, key)
+		if err != nil {
+			return nil, err
+		}
+	}
+	text := object.TextObject
+	if object.Type != "TextObject" {
+		return nil, fmt.Errorf("object is not text")
+	}
+	editor := currentEditor
+	if len(args) > 3 && !args[3].IsNull() {
+		data, err := bytesFromJS(args[3])
+		if err != nil {
+			return nil, err
+		}
+		editor = ofdgo.NewEditor()
+		text.Font, err = editor.AddFont(FontFile{Data: data}, 0)
+		if err != nil {
+			return nil, err
+		}
+	}
+	if len(args) > 4 && args[4].Float() != text.Size {
+		var x, y float64
+		if strings.Contains(key, "/") {
+			x, _ = strconv.ParseFloat(text.TextCode[0].X, 64)
+			y, _ = strconv.ParseFloat(text.TextCode[0].Y, 64)
+		}
+		text.Size = args[4].Float()
+		_, layout := text.TextLayout()
+		if err := editor.LayoutText(&text, args[2].String(), layout); err != nil {
+			return nil, err
+		}
+		if strings.Contains(key, "/") {
+			baseline, _ := strconv.ParseFloat(text.TextCode[0].Y, 64)
+			for i := range text.TextCode {
+				code := &text.TextCode[i]
+				cx, _ := strconv.ParseFloat(code.X, 64)
+				cy, _ := strconv.ParseFloat(code.Y, 64)
+				code.X, code.Y = fmt.Sprint(cx+x), fmt.Sprint(cy+y-baseline)
+			}
+		}
+	} else if err := editor.RewriteText(&text, args[2].String()); err != nil {
+		return nil, err
+	}
+	var runs []any
+	var x, y float64
+	value, offset := []rune(text.Text()), 0
+	for _, code := range text.TextCode {
+		if code.X != "" {
+			x, _ = strconv.ParseFloat(code.X, 64)
+		}
+		if code.Y != "" {
+			y, _ = strconv.ParseFloat(code.Y, 64)
+		}
+		line := offset < len(value) && value[offset] == '\n'
+		if line {
+			offset++
+		}
+		content := (ofdgo.TextObject{TextCode: []ofdgo.TextCode{code}}).Text()
+		runs = append(runs, map[string]any{"text": content, "x": x, "y": y, "dx": code.GetDeltaX(), "dy": code.GetDeltaY(), "line": line})
+		offset += len([]rune(content))
+	}
+	scale := text.HScale
+	if scale == 0 {
+		scale = 1
+	}
+	return map[string]any{"runs": runs, "scale": scale, "weight": text.Weight, "italic": text.Italic}, nil
+}
+
 // replaceImage 替换图片资源并更新预览
 // 入参: args 页码、对象标识、图片数据和适应方式
 // 返回: any 文档信息, error 错误信息
@@ -2704,6 +2800,24 @@ func updateText(args []js.Value) (any, error) {
 		}
 	}
 	if !args[2].IsNull() {
+		if args[4].Float() == object.TextObject.Size {
+			style := ofdgo.TextStyle{Font: object.TextObject.Font}
+			if !args[5].IsNull() {
+				var fill ofdgo.FillColor
+				if err := setEditorColor(&fill, args[5].String()); err != nil {
+					return nil, err
+				}
+				style.Color = fill.Value
+			}
+			revision := currentEditor.Revision()
+			if err := currentEditor.UpdateTextContent(page, id, args[2].String(), style); err != nil {
+				return nil, err
+			}
+			if currentEditor.Revision() == revision {
+				return editorSummary(), nil
+			}
+			return previewEditor(currentEditor, currentSession.Renderer.RenderAnnotations)
+		}
 		object.TextObject.Size = args[4].Float()
 		_, layout := object.TextObject.TextLayout()
 		if err := currentEditor.LayoutText(&object.TextObject, args[2].String(), layout); err != nil {
diff --git a/ofdgo_editor.go b/ofdgo_editor.go
index 1e6593e..c785a34 100644
--- a/ofdgo_editor.go
+++ b/ofdgo_editor.go
@@ -47,6 +47,7 @@ type Editor struct {
 	resources       []editorResource
 	fonts           map[string]*font.SFNT
 	fontFS          []fs.FS
+	fontRenderer    *Renderer
 	images          map[string]image.Point
 	resourceID      map[editorResourceKey]string
 	maxID           int
@@ -60,10 +61,11 @@ type Editor struct {
 	outlines        []byte
 }
 
-// SetFontFS 设置几何度量使用的外部字体来源，与预览渲染器保持一致，不嵌入或替换文档字体
+// SetFontFS 设置编辑与几何度量使用的外部字体来源，不嵌入或替换文档字体
 // 入参: fsys 字体文件系统，空参数恢复默认来源
 func (e *Editor) SetFontFS(fsys ...fs.FS) {
 	e.fontFS = slices.Clone(fsys)
+	e.fontRenderer = nil
 }
 
 // editorResource 文档内嵌资源
@@ -1150,7 +1152,7 @@ func (e *Editor) prepareText(obj *TextObject) error {
 		return err
 	}
 	if !finite(obj.Size) || obj.Size <= 0 {
-		return fmt.Errorf("text requires an embedded font and a positive finite size")
+		return fmt.Errorf("text requires a positive finite size")
 	}
 	if len(obj.TextCode) == 0 {
 		return fmt.Errorf("text codes are empty")
@@ -1197,7 +1199,7 @@ func (e *Editor) prepareText(obj *TextObject) error {
 		}
 		for _, delta := range []string{code.DeltaX, code.DeltaY} {
 			if delta != "" {
-				if err := creationDeltas(delta, len(runes)-1); err != nil {
+				if err := creationDeltas(delta); err != nil {
 					return fmt.Errorf("invalid text delta: %w", err)
 				}
 			}
@@ -1214,19 +1216,16 @@ func (e *Editor) prepareText(obj *TextObject) error {
 }
 
 // creationDeltas 校验文字位移数组及g重复编码
-// 入参: value 位移数组, count 所需位移数量
+// 入参: value 位移数组
 // 返回: error 错误信息
-func creationDeltas(value string, count int) error {
+func creationDeltas(value string) error {
 	fields := strings.Fields(value)
-	numbers := 0
 	for i := 0; i < len(fields); i++ {
-		repeat := 1
 		if fields[i] == "g" {
 			if i+2 >= len(fields) {
 				return fmt.Errorf("incomplete delta repetition")
 			}
-			var err error
-			repeat, err = strconv.Atoi(fields[i+1])
+			repeat, err := strconv.Atoi(fields[i+1])
 			if err != nil || repeat <= 0 {
 				return fmt.Errorf("invalid delta repetition")
 			}
@@ -1235,13 +1234,6 @@ func creationDeltas(value string, count int) error {
 		if _, err := creationNumbers(fields[i], 1); err != nil {
 			return err
 		}
-		if repeat > count-numbers {
-			return fmt.Errorf("too many text deltas")
-		}
-		numbers += repeat
-	}
-	if numbers != count {
-		return fmt.Errorf("expected %d text deltas", count)
 	}
 	return nil
 }
diff --git a/ofdgo_editor_composite.go b/ofdgo_editor_composite.go
index 7dc15d0..e9a2cc5 100644
--- a/ofdgo_editor_composite.go
+++ b/ofdgo_editor_composite.go
@@ -549,9 +549,12 @@ func (e *Editor) measureCompositeMembers(renderer *Renderer, nodes []*editorComp
 			if err := e.prepareText(&text); err != nil {
 				capability.ReasonCode, capability.Reason = editReason(err), err.Error()
 				errors.As(err, &capability.MissingGlyphs)
-			} else if _, err := text.TextFrame(); err == nil {
-				capability.Reflow = text.ReadDirection == 0 && text.CharDirection == 0
-				capability.LayoutKnown = text.layout != nil
+			} else {
+				capability.TextContent = text.ReadDirection == 0 && text.CharDirection == 0
+				if _, err := text.TextFrame(); err == nil {
+					capability.Reflow = capability.TextContent
+					capability.LayoutKnown = text.layout != nil
+				}
 			}
 		}
 		if transform && node.object.Type == "ImageObject" && bounds.box.W > 0 && bounds.box.H > 0 {
diff --git a/ofdgo_editor_composite_text.go b/ofdgo_editor_composite_text.go
index 4c4da78..44b534d 100644
--- a/ofdgo_editor_composite_text.go
+++ b/ofdgo_editor_composite_text.go
@@ -20,8 +20,8 @@ import (
 	"strconv"
 )
 
-// UpdateCompositeText 修改内部普通横向文字，保留首行起点、变换、裁剪及未修改属性
-// 复杂字形定位不自动重排，空样式保留原字体、字号和颜色
+// UpdateCompositeText 修改内部普通横向文字，原文保留定位，已知段落按会话选项重排
+// 空样式保留原字体、字号和颜色，显式改变字号时重新排版并保留首行基线
 // 入参: page 页面索引, path 父复合路径, index 成员序号, value 文字, style 文字样式增量
 // 返回: error 错误信息
 func (e *Editor) UpdateCompositeText(page int, path ObjectPath, index int, value string, style TextStyle) error {
@@ -100,7 +100,12 @@ func (e *Editor) updateCompositeText(node *editorCompositeNode, member Composite
 		}
 		object.TextObject.Boundary, object.TextObject.CTM = text.Boundary, text.CTM
 	}
-	if options != nil || content != original || style.Size != 0 && style.Size != text.Size {
+	if options == nil && frame == nil && state.layout == nil && (style.Size == 0 || style.Size == text.Size) && content != original {
+		if err := e.RewriteText(&text, content); err != nil {
+			return err
+		}
+		object.TextObject.TextCode = text.TextCode
+	} else if options != nil || content != original || style.Size != 0 && style.Size != text.Size {
 		if style.Size != 0 {
 			text.Size = style.Size
 		}
diff --git a/ofdgo_editor_error.go b/ofdgo_editor_error.go
index f3fe5aa..a4d152e 100644
--- a/ofdgo_editor_error.go
+++ b/ofdgo_editor_error.go
@@ -32,6 +32,8 @@ const (
 	EditFontUnavailable EditReason = "fontUnavailable"
 	// EditMissingGlyphs 字体缺少文字所需字形
 	EditMissingGlyphs EditReason = "missingGlyphs"
+	// EditLayoutRequired 内容变化需要显式选择段落排版
+	EditLayoutRequired EditReason = "layoutRequired"
 	// EditInvalidObject 对象数据未通过校验
 	EditInvalidObject EditReason = "invalidObject"
 )
diff --git a/ofdgo_editor_open.go b/ofdgo_editor_open.go
index e7ef72f..08789e0 100644
--- a/ofdgo_editor_open.go
+++ b/ofdgo_editor_open.go
@@ -26,6 +26,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/tdewolff/canvas"
 	"github.com/tdewolff/font"
 )
 
@@ -64,6 +65,7 @@ type editorSourcePage struct {
 // ObjectCapabilities 已有对象可执行的操作，Reason说明受限原因
 // Update表示完整替换内容，ReplaceFont表示可显式替换文字字体，Transform表示保留文字定位的几何变换，Order仅限同一图层或末级页块
 // Arrange表示可准确度量对齐与旋转范围；Reflow表示可重排文字，LayoutKnown表示段落选项可恢复
+// TextContent表示可修改文字内容，未知段落保持原定位，不自动重排
 // FitImage表示可按原始图片比例适应或填充现有边界
 // ResetCrop表示有可单独还原的会话裁剪
 // Paint表示可独立修改纯色填充和描边，不要求重新排版文字
@@ -72,6 +74,7 @@ type editorSourcePage struct {
 // Ungroup表示可移除组合容器并保留内部内容，Stretch表示图片及纯图片组合可独立调整宽高
 type ObjectCapabilities struct {
 	Update        bool
+	TextContent   bool
 	Paint         bool
 	ReplaceFont   bool
 	ReplaceImage  bool
@@ -369,6 +372,7 @@ func (e *Editor) ObjectCapabilities(page int, id string) (ObjectCapabilities, er
 	all.ResetCrop = object.Type == "ImageObject" && object.state.crop != nil
 	origin := e.objectOrigin(id)
 	if origin == nil {
+		all.TextContent = all.Reflow
 		all.Stretch = object.Type == "ImageObject"
 		all.ReplaceImage = object.Type == "ImageObject"
 		all.CropImage = all.ReplaceImage
@@ -411,6 +415,7 @@ func (e *Editor) ObjectCapabilities(page int, id string) (ObjectCapabilities, er
 		all.Reason, all.ReasonCode = "image actions cannot be transformed together with the border", EditUnsupportedObject
 	}
 	if object.Type == "TextObject" {
+		all.TextContent = all.Update && object.TextObject.ReadDirection == 0 && object.TextObject.CharDirection == 0
 		all.Arrange = all.Update || e.editorTextMeasurable(object.TextObject)
 		if _, err := object.TextObject.TextFrame(); err != nil {
 			all.Reflow = false
@@ -611,7 +616,7 @@ func editorGeometry(object GraphicObject) (string, string) {
 	return "", ""
 }
 
-// editorFont 按需解析原文档内嵌字体，不用系统回退替换原字体
+// editorFont 按需解析内嵌字体或名称匹配的外部字体，不使用无关回退字体
 // 入参: id 字体资源标识
 // 返回: *font.SFNT 字体, error 错误信息
 func (e *Editor) editorFont(id string) (*font.SFNT, error) {
@@ -619,6 +624,22 @@ func (e *Editor) editorFont(id string) (*font.SFNT, error) {
 		return sfnt, nil
 	}
 	if e.source != nil {
+		definition := e.source.reader.fontCache[id]
+		if definition != nil && definition.FontFile == "" {
+			if e.fontRenderer == nil {
+				e.fontRenderer = NewRenderer(e.source.reader, WithFontFS(e.fontFS...))
+			}
+			style := canvasFontStyle(definition)
+			for _, source := range e.fontRenderer.fontSources(id, definition, style) {
+				if !source.exact {
+					continue
+				}
+				if family := e.fontRenderer.loadFontSource(canvas.NewFontFamily(definition.FontName), source, style); family != nil {
+					return family.Face(12, style).Font.SFNT, nil
+				}
+			}
+			return nil, &EditError{Code: EditFontUnavailable, Err: fmt.Errorf("font %q is unavailable", definition.FontName)}
+		}
 		data, err := e.source.reader.FontData(id)
 		if err != nil {
 			return nil, &EditError{Code: EditFontUnavailable, Err: err}
@@ -630,7 +651,28 @@ func (e *Editor) editorFont(id string) (*font.SFNT, error) {
 		e.fonts[id] = sfnt
 		return sfnt, nil
 	}
-	return nil, &EditError{Code: EditFontUnavailable, Err: fmt.Errorf("embedded font %q not found", id)}
+	return nil, &EditError{Code: EditFontUnavailable, Err: fmt.Errorf("font %q not found", id)}
+}
+
+// FontData 获取编辑使用的字体数据，外部字体不写入文档资源
+// 入参: id 字体资源标识
+// 返回: []byte 独立字体数据, error 错误信息
+func (e *Editor) FontData(id string) ([]byte, error) {
+	for _, resource := range e.resources {
+		if resource.font != nil && resource.font.ID == id {
+			return bytes.Clone(resource.data), nil
+		}
+	}
+	if e.source != nil {
+		if definition := e.source.reader.fontCache[id]; definition != nil && definition.FontFile != "" {
+			return e.source.reader.FontData(id)
+		}
+	}
+	sfnt, err := e.editorFont(id)
+	if err != nil {
+		return nil, err
+	}
+	return sfnt.Write(), nil
 }
 
 // editorTextMeasurable 判断原字形能否在不使用回退字体的情况下度量
@@ -787,7 +829,7 @@ func validateEditorGeometry(object GraphicObject) error {
 			}
 			for _, value := range []string{code.DeltaX, code.DeltaY} {
 				if value != "" {
-					if err := creationDeltas(value, len(textCodeRunes(code.Value))-1); err != nil {
+					if err := creationDeltas(value); err != nil {
 						return err
 					}
 				}
diff --git a/ofdgo_editor_text.go b/ofdgo_editor_text.go
index 95aee4b..0755b92 100644
--- a/ofdgo_editor_text.go
+++ b/ofdgo_editor_text.go
@@ -15,9 +15,11 @@
 package ofdgo
 
 import (
+	"errors"
 	"fmt"
 	"image/color"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/go-text/typesetting/segmenter"
 )
@@ -95,6 +97,186 @@ func (e *Editor) StyleText(page int, ids []string, style TextStyle) error {
 	return e.UpdateObjects(page, updates)
 }
 
+// UpdateTextContent 修改文字内容及样式，原文保留定位，已知段落按会话选项重排
+// 原文等长替换保留全部位移，单个TextCode内增删仅调整局部步进，跨定位段增删需显式重排
+// 入参: page 页面索引, id 文字对象标识, value 新内容, style 样式增量
+// 返回: error 错误信息
+func (e *Editor) UpdateTextContent(page int, id, value string, style TextStyle) error {
+	capability, err := e.ObjectCapabilities(page, id)
+	if err != nil {
+		return err
+	}
+	if !capability.ReplaceFont {
+		return capability.editError()
+	}
+	object, err := e.Object(page, id)
+	if err != nil {
+		return err
+	}
+	updates, err := e.styleTextObjects([]GraphicObject{object}, style)
+	if err != nil {
+		return err
+	}
+	text := &updates[0].TextObject
+	if capability.LayoutKnown {
+		_, layout := text.TextLayout()
+		err = e.LayoutText(text, value, layout)
+	} else {
+		err = e.RewriteText(text, value)
+	}
+	if err != nil {
+		return err
+	}
+	return e.updateObjects(page, updates, true)
+}
+
+// RewriteText 保留普通横向原文的字形定位，不修改对象样式或文档
+// 等长替换保留各字原位；单段增删保留前缀和后缀步进，新增字符沿用局部字距
+// 不跨定位段增删或自动生成新行，复杂字形映射需单独处理
+// 入参: obj 原文字对象, value 新内容
+// 返回: error 错误信息
+func (e *Editor) RewriteText(obj *TextObject, value string) error {
+	if obj.ReadDirection != 0 || obj.CharDirection != 0 || len(obj.CGTransform) != 0 || obj.VScale != 0 || obj.Decoration != "" {
+		return &EditError{Code: EditUnsupportedObject, Err: fmt.Errorf("text positioning is not supported for content editing")}
+	}
+	value = strings.ReplaceAll(strings.ReplaceAll(value, "\r\n", "\n"), "\r", "\n")
+	if !utf8.ValidString(value) || strings.Contains(value, "\t") || strings.Trim(value, "\n") == "" {
+		return fmt.Errorf("text must contain UTF-8 characters without tabs")
+	}
+	check := cloneEditorData(*obj)
+	if err := e.prepareText(&check); err != nil {
+		var missing *MissingGlyphError
+		if !errors.As(err, &missing) {
+			return err
+		}
+	}
+	sfnt, err := e.editorFont(obj.Font)
+	if err != nil {
+		return err
+	}
+	var missing []rune
+	for _, char := range value {
+		if char != '\n' && sfnt.GlyphIndex(char) == 0 {
+			missing = append(missing, char)
+		}
+	}
+	if err := missingGlyphError(obj.Font, missing); err != nil {
+		return err
+	}
+	old, next := []rune(obj.Text()), []rune(value)
+	codes := append([]TextCode(nil), obj.TextCode...)
+	if len(old) == len(next) {
+		offset := 0
+		for i := range codes {
+			if obj.textCodeLineBreak(i) {
+				if next[offset] != '\n' {
+					return &EditError{Code: EditLayoutRequired, Err: fmt.Errorf("changing text lines requires explicit layout")}
+				}
+				offset++
+			}
+			end := offset + len(textCodeRunes(codes[i].Value))
+			content := string(next[offset:end])
+			if strings.Contains(content, "\n") {
+				return &EditError{Code: EditLayoutRequired, Err: fmt.Errorf("changing text lines requires explicit layout")}
+			}
+			if content != string(textCodeRunes(codes[i].Value)) {
+				codes[i].Value = escapeOFDText(content)
+			}
+			offset = end
+		}
+	} else {
+		start := 0
+		for start < min(len(old), len(next)) && old[start] == next[start] {
+			start++
+		}
+		end, nextEnd := len(old), len(next)
+		for end > start && nextEnd > start && old[end-1] == next[nextEnd-1] {
+			end--
+			nextEnd--
+		}
+		if strings.ContainsAny(string(old[start:end])+string(next[start:nextEnd]), "\n") {
+			return &EditError{Code: EditLayoutRequired, Err: fmt.Errorf("changing text lines requires explicit layout")}
+		}
+		offset, changed := 0, false
+		for i := range codes {
+			if obj.textCodeLineBreak(i) {
+				offset++
+			}
+			runes := textCodeRunes(codes[i].Value)
+			limit := offset + len(runes)
+			if start >= offset && end <= limit {
+				from, to := start-offset, end-offset
+				replacement := next[start:nextEnd]
+				content := append(append(append([]rune(nil), runes[:from]...), replacement...), runes[to:]...)
+				if len(content) == 0 {
+					return &EditError{Code: EditLayoutRequired, Err: fmt.Errorf("removing a positioned text run requires explicit layout")}
+				}
+				unit := obj.Size / float64(sfnt.UnitsPerEm())
+				if obj.HScale != 0 {
+					unit *= obj.HScale
+				}
+				advance := func(char rune) float64 { return float64(sfnt.GlyphAdvance(sfnt.GlyphIndex(char))) * unit }
+				if codes[i].DeltaX != "" || codes[i].DeltaY == "" {
+					codes[i].DeltaX = rewriteTextDeltas(codes[i].DeltaX, runes, replacement, from, to, advance)
+				}
+				if codes[i].DeltaY != "" {
+					codes[i].DeltaY = rewriteTextDeltas(codes[i].DeltaY, runes, replacement, from, to, func(rune) float64 { return 0 })
+				}
+				codes[i].Value = escapeOFDText(string(content))
+				changed = true
+				break
+			}
+			offset = limit
+		}
+		if !changed {
+			return &EditError{Code: EditLayoutRequired, Err: fmt.Errorf("editing across positioned text runs requires explicit layout")}
+		}
+	}
+	check = *obj
+	check.TextCode = codes
+	if err := validateEditorGeometry(GraphicObject{Type: "TextObject", TextObject: check}); err != nil {
+		return err
+	}
+	obj.TextCode, obj.layout = codes, nil
+	return nil
+}
+
+// rewriteTextDeltas 局部替换字符步进，保留未修改字符及末尾附加位移
+// 入参: value 原位移, old 原字符, replacement 替换字符, start 起点, end 终点, advance 字体步进
+// 返回: string 更新后的位移数组
+func rewriteTextDeltas(value string, old, replacement []rune, start, end int, advance func(rune) float64) string {
+	deltas := parseFloatsWithG(value)
+	steps := make([]float64, len(old))
+	for i, char := range old {
+		steps[i] = advance(char)
+		if i < len(old)-1 || len(deltas) >= len(old) {
+			if delta, ok := textDelta(deltas, i); ok {
+				steps[i] = delta
+			}
+		}
+	}
+	tracking := 0.0
+	if len(old) > 0 && (len(old) > 1 || len(deltas) != 0) {
+		index := min(start, max(0, len(old)-2))
+		tracking = steps[index] - advance(old[index])
+	}
+	result := append([]float64(nil), steps[:start]...)
+	for _, char := range replacement {
+		result = append(result, advance(char)+tracking)
+	}
+	result = append(result, steps[end:]...)
+	if len(deltas) < len(old) {
+		result = result[:len(result)-1]
+	} else {
+		result = append(result, deltas[len(old):]...)
+	}
+	numbers := make([]string, len(result))
+	for i, delta := range result {
+		numbers[i] = ofdNumber(delta)
+	}
+	return strings.Join(numbers, " ")
+}
+
 // styleTextObjects 生成文字样式副本，不提交文档或历史
 // 入参: objects 原文字对象, style 样式增量
 // 返回: []GraphicObject 更新对象, error 错误信息