feat(edit-pdf): add editing for existing PDF text

messages/en.json

@@ -1755,6 +1755,14 @@
       "saveError": "Failed to save PDF. Please use the export button in the toolbar.",
       "savingMessage": "Saving PDF with annotations...",
       "successMessage": "PDF saved successfully! Click the download button to save your edited file.",
+      "textHistory": "Text change history",
+      "textUndo": "Undo text",
+      "textRedo": "Redo text",
+      "textUndoApplied": "The last text change was undone.",
+      "textRedoApplied": "The text change was redone.",
+      "overflowAppliedWarning": "The replacement text exceeds the original area. Review the result visually before exporting.",
+      "fallbackFontWarning": "The original font could not be reused and a fallback was used. Review the characters and spacing.",
+      "signatureInvalidatedWarning": "This PDF contained digital signatures. Editing its content invalidates the existing signatures.",
       "redactWarningTitle": "Redaction Mode Active",
       "redactWarningDescription": "Select areas to permanently remove content. Redacted content cannot be recovered after saving.",
       "toolbar": {

messages/es.json

@@ -1754,6 +1754,14 @@
       "saveError": "No se pudo guardar el PDF. Utilice el botón exportar en la barra de herramientas.",
       "savingMessage": "Guardando PDF con anotaciones...",
       "successMessage": "¡PDF guardado exitosamente! Haga clic en el botón de descarga para guardar su archivo editado.",
+      "textHistory": "Historial de cambios de texto",
+      "textUndo": "Deshacer texto",
+      "textRedo": "Rehacer texto",
+      "textUndoApplied": "Se ha deshecho el último cambio de texto.",
+      "textRedoApplied": "Se ha rehecho el cambio de texto.",
+      "overflowAppliedWarning": "El texto sustituido excede el área original. Revise visualmente el resultado antes de exportar.",
+      "fallbackFontWarning": "La fuente original no pudo reutilizarse y se empleó una alternativa. Revise los caracteres y el espaciado.",
+      "signatureInvalidatedWarning": "Este PDF contenía firmas digitales. La edición del contenido invalida sus firmas existentes.",
       "redactWarningTitle": "Modo de redacción activo",
       "redactWarningDescription": "Seleccione áreas para eliminar contenido permanentemente. El contenido redactado no se puede recuperar después de guardarlo.",
       "toolbar": {

src/__tests__/lib/pdf/replace-existing-text.test.ts

@@ -0,0 +1,138 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import {
+  replaceExistingText,
+} from '@/lib/pdf/processors/replace-existing-text';
+import type { TextMatch } from '@/lib/pdf/processors/find-and-redact';
+import { loadPyMuPDF } from '@/lib/pdf/pymupdf-loader';
+
+vi.mock('@/lib/pdf/pymupdf-loader', () => ({
+  loadPyMuPDF: vi.fn(),
+}));
+
+const matches: TextMatch[] = [
+  {
+    page: 1,
+    text: 'Original',
+    x: 10,
+    y: 20,
+    width: 50,
+    height: 12,
+    id: 'first',
+    selected: true,
+  },
+  {
+    page: 2,
+    text: 'Original',
+    x: 15,
+    y: 25,
+    width: 50,
+    height: 12,
+    id: 'second',
+    selected: false,
+  },
+];
+
+describe('replaceExistingText', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('passes only selected coordinates to the local PyMuPDF engine', async () => {
+    const output = new Blob(['edited'], { type: 'application/pdf' });
+    const diagnostics = {
+      usedFallbackFont: false,
+      overflowDetected: false,
+      hasDigitalSignatures: false,
+    };
+    const replaceExistingTextMock = vi.fn().mockResolvedValue({
+      blob: output,
+      diagnostics,
+    });
+    vi.mocked(loadPyMuPDF).mockResolvedValue({
+      replaceExistingText: replaceExistingTextMock,
+    });
+    const file = new File(['pdf'], 'sample.pdf', { type: 'application/pdf' });
+
+    const result = await replaceExistingText(file, matches, {
+      replacementText: 'Updated',
+      selectedMatchIds: ['first'],
+    });
+
+    expect(result).toEqual({
+      success: true,
+      result: output,
+      replacedCount: 1,
+      diagnostics,
+    });
+    expect(replaceExistingTextMock).toHaveBeenCalledWith(
+      file,
+      [{ page: 1, x: 10, y: 20, width: 50, height: 12 }],
+      'Updated',
+      'preserve'
+    );
+  });
+
+  it('passes the requested overflow strategy to the engine', async () => {
+    const output = new Blob(['edited'], { type: 'application/pdf' });
+    const diagnostics = {
+      usedFallbackFont: true,
+      overflowDetected: true,
+      hasDigitalSignatures: true,
+    };
+    const replaceExistingTextMock = vi.fn().mockResolvedValue({
+      blob: output,
+      diagnostics,
+    });
+    vi.mocked(loadPyMuPDF).mockResolvedValue({
+      replaceExistingText: replaceExistingTextMock,
+    });
+
+    const result = await replaceExistingText(
+      new File(['pdf'], 'sample.pdf', { type: 'application/pdf' }),
+      matches,
+      {
+        replacementText: 'A much longer replacement',
+        selectedMatchIds: ['first'],
+        fitMode: 'shrink',
+      }
+    );
+
+    expect(replaceExistingTextMock).toHaveBeenCalledWith(
+      expect.any(File),
+      [{ page: 1, x: 10, y: 20, width: 50, height: 12 }],
+      'A much longer replacement',
+      'shrink'
+    );
+    expect(result.diagnostics).toEqual(diagnostics);
+  });
+
+  it('rejects an empty selection without loading the PDF engine', async () => {
+    const file = new File(['pdf'], 'sample.pdf', { type: 'application/pdf' });
+
+    const result = await replaceExistingText(file, matches, {
+      replacementText: 'Updated',
+      selectedMatchIds: ['missing'],
+    });
+
+    expect(result.success).toBe(false);
+    expect(result.replacedCount).toBe(0);
+    expect(loadPyMuPDF).not.toHaveBeenCalled();
+  });
+
+  it('reports engine errors without returning a partial PDF', async () => {
+    vi.mocked(loadPyMuPDF).mockResolvedValue({
+      replaceExistingText: vi.fn().mockRejectedValue(new Error('WASM failed')),
+    });
+    const file = new File(['pdf'], 'sample.pdf', { type: 'application/pdf' });
+
+    const result = await replaceExistingText(file, matches, {
+      replacementText: 'Updated',
+    });
+
+    expect(result).toEqual({
+      success: false,
+      replacedCount: 0,
+      error: 'WASM failed',
+    });
+  });
+});