diff --git a/packages/superdoc/package.json b/packages/superdoc/package.json
index 912171bb6d..25a305bc5b 100644
--- a/packages/superdoc/package.json
+++ b/packages/superdoc/package.json
@@ -135,7 +135,8 @@
     "pack:local": "pnpm run pack:es",
     "pack": "node ./scripts/pack-output.cjs clean && pnpm run build:es && pnpm pack && node ./scripts/pack-output.cjs finalize",
     "pack:es": "node ./scripts/pack-output.cjs clean && pnpm run build:es && pnpm pack && node ./scripts/pack-output.cjs finalize",
-    "test": "vitest"
+    "test": "vitest",
+    "test:external-docx": "node scripts/run-external-docx.mjs"
   },
   "dependencies": {
     "@types/mdast": "catalog:",
diff --git a/packages/superdoc/scripts/run-external-docx.mjs b/packages/superdoc/scripts/run-external-docx.mjs
new file mode 100644
index 0000000000..8ce3f4b8a6
--- /dev/null
+++ b/packages/superdoc/scripts/run-external-docx.mjs
@@ -0,0 +1,112 @@
+import { existsSync, statSync } from 'node:fs';
+import { mkdir, mkdtemp } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { dirname, extname, join, resolve } from 'node:path';
+import { spawnSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+
+const usage = `Usage:
+  pnpm --filter superdoc test:external-docx -- --fixture <input.docx> [--output <roundtrip.docx>] [--evidence <evidence.json>]
+`;
+
+const parseOptions = (args) => {
+  if (args.includes('--help')) return { help: true };
+
+  const values = new Map();
+  const allowed = new Set(['--fixture', '--output', '--evidence']);
+  for (let index = 0; index < args.length; index += 2) {
+    const flag = args[index];
+    const value = args[index + 1];
+    if (!flag || !allowed.has(flag)) throw new Error(`Unknown option: ${flag ?? ''}`);
+    if (!value) throw new Error(`${flag} requires a value`);
+    if (values.has(flag)) throw new Error(`${flag} may only be provided once`);
+    values.set(flag, value);
+  }
+
+  const fixture = values.get('--fixture');
+  if (!fixture) throw new Error('--fixture is required');
+  return {
+    fixture: resolve(fixture),
+    output: values.has('--output') ? resolve(values.get('--output')) : null,
+    evidence: values.has('--evidence') ? resolve(values.get('--evidence')) : null,
+  };
+};
+
+const main = async () => {
+  let options;
+  try {
+    const args = process.argv.slice(2);
+    if (args[0] === '--') args.shift();
+    options = parseOptions(args);
+  } catch (error) {
+    console.error(error.message);
+    console.error(usage);
+    return 1;
+  }
+
+  if (options.help) {
+    console.log(usage);
+    return 0;
+  }
+
+  if (extname(options.fixture).toLowerCase() !== '.docx') {
+    console.error(`Fixture must be a .docx file: ${options.fixture}`);
+    return 1;
+  }
+  if (!existsSync(options.fixture) || !statSync(options.fixture).isFile()) {
+    console.error(`Fixture does not exist: ${options.fixture}`);
+    return 1;
+  }
+
+  const artifactsDirectory =
+    options.output && options.evidence ? null : await mkdtemp(join(tmpdir(), 'superdoc-external-docx-'));
+  const output = options.output ?? join(artifactsDirectory, 'roundtrip.docx');
+  const evidence = options.evidence ?? join(artifactsDirectory, 'evidence.json');
+  if (extname(output).toLowerCase() !== '.docx') {
+    console.error(`Output must be a .docx file: ${output}`);
+    return 1;
+  }
+  if (extname(evidence).toLowerCase() !== '.json') {
+    console.error(`Evidence must be a .json file: ${evidence}`);
+    return 1;
+  }
+  if (new Set([options.fixture, output, evidence]).size !== 3) {
+    console.error('Fixture, output, and evidence paths must be different');
+    return 1;
+  }
+  const existingArtifact = [output, evidence].find((path) => existsSync(path));
+  if (existingArtifact) {
+    console.error(`Artifact path already exists: ${existingArtifact}`);
+    return 1;
+  }
+  await Promise.all([mkdir(dirname(output), { recursive: true }), mkdir(dirname(evidence), { recursive: true })]);
+
+  console.log(`Fixture: ${options.fixture}`);
+  console.log(`Round-trip DOCX: ${output}`);
+  console.log(`Evidence: ${evidence}`);
+
+  const packageRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..');
+  const pnpmCommand = process.platform === 'win32' ? 'pnpm.cmd' : 'pnpm';
+  const result = spawnSync(
+    pnpmCommand,
+    ['exec', 'vitest', 'run', '--config', 'tests/external-docx/vitest.config.js', '--reporter=verbose'],
+    {
+      cwd: packageRoot,
+      stdio: 'inherit',
+      env: {
+        ...process.env,
+        SUPERDOC_TEST_DOCX: options.fixture,
+        SUPERDOC_TEST_OUTPUT: output,
+        SUPERDOC_TEST_EVIDENCE: evidence,
+      },
+    },
+  );
+
+  if (result.error) {
+    console.error(`Unable to start Vitest: ${result.error.message}`);
+    return 1;
+  }
+  return result.status ?? 1;
+};
+
+process.exitCode = await main();
diff --git a/packages/superdoc/tests/external-docx/README.md b/packages/superdoc/tests/external-docx/README.md
new file mode 100644
index 0000000000..c4a600a417
--- /dev/null
+++ b/packages/superdoc/tests/external-docx/README.md
@@ -0,0 +1,21 @@
+# External DOCX feedback loop
+
+Run an externally generated DOCX through SuperDoc import, comment projection, export, and re-import:
+
+```bash
+pnpm --filter superdoc test:external-docx -- \
+  --fixture /absolute/path/input.docx
+```
+
+The command prints temporary paths for the exported DOCX and JSON evidence. Keep artifacts at explicit paths when another tool, such as Microsoft Word, needs to inspect them:
+
+```bash
+pnpm --filter superdoc test:external-docx -- \
+  --fixture /absolute/path/input.docx \
+  --output /tmp/superdoc-roundtrip.docx \
+  --evidence /tmp/superdoc-roundtrip.json
+```
+
+The fixture must contain at least one comment. The run fails when comment import is empty or a comment disappears during sidebar projection or export. The evidence records input and output hashes, rendered comment HTML, and imported node types.
+
+The DOCX editor and comments store are real. User, selection, collaboration, and comment-model host plumbing are mocked so this test stays focused on document conversion and sidebar projection. Generated fixtures and artifacts stay outside the repository.
diff --git a/packages/superdoc/tests/external-docx/external-docx.fixture.js b/packages/superdoc/tests/external-docx/external-docx.fixture.js
new file mode 100644
index 0000000000..6d4511c57b
--- /dev/null
+++ b/packages/superdoc/tests/external-docx/external-docx.fixture.js
@@ -0,0 +1,177 @@
+import { createHash } from 'node:crypto';
+import { readFile, writeFile } from 'node:fs/promises';
+import { createPinia, defineStore, setActivePinia } from 'pinia';
+import { reactive, ref } from 'vue';
+
+vi.mock('@superdoc/stores/superdoc-store', () => {
+  const documents = ref([]);
+  const user = reactive({ name: 'Fixture runner', email: 'fixture-runner@superdoc.dev' });
+  const activeSelection = reactive({ documentId: 'external-docx', selectionBounds: {} });
+  const selectionPosition = reactive({ source: null });
+  const getDocument = (id) => documents.value.find((document) => document.id === id);
+  const useMockStore = defineStore('superdoc', () => ({
+    documents,
+    user,
+    activeSelection,
+    selectionPosition,
+    getDocument,
+  }));
+
+  return {
+    useSuperdocStore: useMockStore,
+    __fixtureSuperdoc: {
+      documents,
+      user,
+      activeSelection,
+      selectionPosition,
+      emit: vi.fn(),
+      config: { isInternal: false },
+    },
+  };
+});
+
+vi.mock('@superdoc/components/CommentsLayer/use-comment', () => ({
+  default: vi.fn((params = {}) => {
+    const selection = params.selection || { source: 'external-docx', selectionBounds: {} };
+    return {
+      ...params,
+      selection,
+      getValues: () => ({ ...params, selection }),
+      setText: vi.fn(),
+    };
+  }),
+}));
+
+vi.mock('@superdoc/core/collaboration/helpers.js', () => ({ syncCommentsToClients: vi.fn() }));
+vi.mock('@superdoc/helpers/group-changes.js', () => ({ groupChanges: vi.fn(() => []) }));
+
+import { useCommentsStore } from '@superdoc/stores/comments-store.js';
+import { __fixtureSuperdoc } from '@superdoc/stores/superdoc-store';
+import { Editor } from '@superdoc/super-editor';
+import { initTestEditor } from '@tests/helpers/helpers.js';
+
+const requiredPath = (name) => {
+  const value = process.env[name];
+  if (!value)
+    throw new Error(`${name} is required. Run this fixture through pnpm --filter superdoc test:external-docx.`);
+  return value;
+};
+
+const sha256 = (bytes) => createHash('sha256').update(bytes).digest('hex');
+
+const toBuffer = async (value) => {
+  if (Buffer.isBuffer(value)) return value;
+  if (value instanceof ArrayBuffer) return Buffer.from(value);
+  if (ArrayBuffer.isView(value)) return Buffer.from(value.buffer, value.byteOffset, value.byteLength);
+  if (typeof value?.arrayBuffer === 'function') return Buffer.from(await value.arrayBuffer());
+  throw new TypeError('Editor.exportDocx returned an unsupported value');
+};
+
+const collectTypes = (value) => {
+  const types = [];
+  const visit = (node) => {
+    if (Array.isArray(node)) return node.forEach(visit);
+    if (!node || typeof node !== 'object') return;
+    if (typeof node.type === 'string') types.push(node.type);
+    if (Array.isArray(node.content)) node.content.forEach(visit);
+  };
+  visit(value);
+  return types;
+};
+
+const commentId = (comment) => String(comment?.commentId ?? '');
+const sortedCommentIds = (comments) => comments.map(commentId).sort();
+const sameCommentIds = (left, right) => {
+  const leftIds = sortedCommentIds(left);
+  const rightIds = sortedCommentIds(right);
+  return leftIds.length === rightIds.length && leftIds.every((id, index) => id === rightIds[index]);
+};
+
+describe('external DOCX feedback loop', () => {
+  let editor;
+  let reimportEditor;
+
+  beforeEach(() => {
+    setActivePinia(createPinia());
+    __fixtureSuperdoc.documents.value = [{ id: 'external-docx', type: 'docx' }];
+  });
+
+  afterEach(() => {
+    editor?.destroy();
+    reimportEditor?.destroy();
+  });
+
+  it('imports, projects comments, exports, and re-imports the document', async () => {
+    const fixturePath = requiredPath('SUPERDOC_TEST_DOCX');
+    const outputPath = requiredPath('SUPERDOC_TEST_OUTPUT');
+    const evidencePath = requiredPath('SUPERDOC_TEST_EVIDENCE');
+    const fixture = await readFile(fixturePath);
+    const [docx, media, mediaFiles, fonts] = await Editor.loadXmlData(fixture, true);
+    ({ editor } = initTestEditor({ content: docx, media, mediaFiles, fonts, documentId: 'external-docx' }));
+
+    const importedComments = editor.converter.comments ?? [];
+    const store = useCommentsStore();
+    await store.processLoadedDocxComments({
+      superdoc: __fixtureSuperdoc,
+      editor,
+      comments: importedComments,
+      documentId: 'external-docx',
+    });
+    const projectedComments = [...store.commentsList];
+
+    const exported = await editor.exportDocx({
+      comments: store.translateCommentsForExport(),
+      commentsType: 'external',
+    });
+    const exportedBytes = await toBuffer(exported);
+    await writeFile(outputPath, exportedBytes);
+
+    const [reimportedDocx, reimportedMedia, reimportedMediaFiles, reimportedFonts] = await Editor.loadXmlData(
+      exportedBytes,
+      true,
+    );
+    ({ editor: reimportEditor } = initTestEditor({
+      content: reimportedDocx,
+      media: reimportedMedia,
+      mediaFiles: reimportedMediaFiles,
+      fonts: reimportedFonts,
+      documentId: 'external-docx-reimported',
+    }));
+    const reimportedComments = reimportEditor.converter.comments ?? [];
+    const commentsImported = importedComments.length > 0;
+    const projectionPreserved = sameCommentIds(projectedComments, importedComments);
+    const roundTripPreserved = sameCommentIds(reimportedComments, importedComments);
+
+    const evidence = {
+      schemaVersion: '1.0',
+      input: { path: fixturePath, bytes: fixture.byteLength, sha256: sha256(fixture) },
+      output: { path: outputPath, bytes: exportedBytes.byteLength, sha256: sha256(exportedBytes) },
+      comments: {
+        imported: importedComments.map((comment) => ({
+          id: commentId(comment),
+          nodeTypes: collectTypes(comment.elements),
+        })),
+        projected: projectedComments.map((comment) => ({
+          id: commentId(comment),
+          html: comment.commentText ?? null,
+          nodeTypes: collectTypes(comment.docxCommentJSON),
+        })),
+        reimported: reimportedComments.map((comment) => ({
+          id: commentId(comment),
+          nodeTypes: collectTypes(comment.elements),
+        })),
+      },
+      checks: {
+        commentsImported,
+        projectionPreserved,
+        roundTripPreserved,
+      },
+    };
+    await writeFile(evidencePath, `${JSON.stringify(evidence, null, 2)}\n`);
+
+    expect(exportedBytes.byteLength).toBeGreaterThan(0);
+    expect(commentsImported, 'No comments were imported from the fixture').toBe(true);
+    expect(projectionPreserved, 'Comment identities changed during sidebar projection').toBe(true);
+    expect(roundTripPreserved, 'Comment identities changed after export and re-import').toBe(true);
+  });
+});
diff --git a/packages/superdoc/tests/external-docx/vitest.config.js b/packages/superdoc/tests/external-docx/vitest.config.js
new file mode 100644
index 0000000000..fc3c30efbf
--- /dev/null
+++ b/packages/superdoc/tests/external-docx/vitest.config.js
@@ -0,0 +1,12 @@
+import { mergeConfig } from 'vitest/config';
+import packageConfigFactory from '../../vite.config.js';
+
+const packageConfig = packageConfigFactory({ mode: 'test', command: 'serve' });
+
+export default mergeConfig(packageConfig, {
+  test: {
+    include: ['tests/external-docx/external-docx.fixture.js'],
+    retry: 0,
+    testTimeout: 60_000,
+  },
+});