feat: add zero-config docx2pdf demo

Adds a `demo` command that converts a bundled sample DOCX to PDF using
whatever backend is installed, giving the suite a uniform first-run
(matching template-vault/draft/compare/sign). Backend-dependent by design:
if no backend is present it prints the install recommendation and exits 3,
otherwise it converts and reports the backend + output. Ships
src/demo-sample.docx; usage text + a bin-level test added. 111 tests pass.

Author: DrBaher

src/cli.js

@@ -216,6 +216,8 @@ function getCapabilities() {
 }
 
 function main(argv) {
+  if (argv[0] === "demo") return runDemo();
+
   const options = parseArgs(argv);
 
   if (options.help) {
@@ -381,6 +383,40 @@ function printSetupHelp() {
   process.stderr.write(lines.join("\n") + "\n");
 }
 
+// Zero-config first run: convert a bundled sample DOCX to PDF using whatever
+// backend is installed. If none is, explain what to install (the conversion
+// itself is backend-dependent, so the demo is best-effort by design).
+function runDemo() {
+  const os = require("node:os");
+  const sampleSrc = path.join(__dirname, "demo-sample.docx");
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "docx2pdf-demo-"));
+  const input = path.join(tmpDir, "sample.docx");
+  fs.copyFileSync(sampleSrc, input);
+
+  process.stderr.write("docx2pdf demo — converting a bundled sample DOCX to PDF.\n");
+
+  if (!getAvailableBackends().length) {
+    process.stderr.write("\nNo PDF backend is installed yet, so the demo can't render the sample.\n");
+    printSetupHelp();
+    try { fs.rmSync(tmpDir, { recursive: true, force: true }); } catch { /* best-effort */ }
+    return EXIT.MISSING_DEP;
+  }
+
+  const output = path.join(tmpDir, "sample.pdf");
+  try {
+    const result = convertDocxToPdf({ input, output, backend: "auto", overwrite: true });
+    const bytes = fs.statSync(result.output).size;
+    process.stdout.write(`\n✓ Converted the sample DOCX to PDF (${bytes} bytes) via the '${result.backend}' backend.\n`);
+    process.stdout.write(`  ${result.output}\n`);
+    process.stdout.write("\nNow try your own file:\n  docx2pdf your.docx out.pdf\n  docx2pdf --doctor            # see all detected backends\n");
+    return 0;
+  } catch (err) {
+    process.stderr.write(`\nDemo conversion failed: ${err.message}\n`);
+    try { fs.rmSync(tmpDir, { recursive: true, force: true }); } catch { /* best-effort */ }
+    return err.exitCode || EXIT.CONVERT_FAIL;
+  }
+}
+
 if (require.main === module) {
   Promise.resolve()
     .then(() => main(process.argv.slice(2)))

src/demo-sample.docx

@@ -636,6 +636,7 @@ function usageText() {
 Usage:
   docx2pdf [options] <input.docx> [output.pdf]
   docx2pdf [options] --out-dir <dir> <input.docx>...
+  docx2pdf demo                            zero-config: convert a bundled sample
 
 Options:
   --backend <auto|libreoffice|gotenberg|convertapi|pages|word|textutil-cups>

src/index.js

@@ -448,3 +448,15 @@ test("single-file --json success includes outputBytes and durationMs", (t) => {
     fs.rmSync(tempDir, { recursive: true, force: true });
   }
 });
+
+test("demo: zero-config command runs the bundled sample", () => {
+  const r = runCli(["demo"]);
+  assert.match(r.stderr, /docx2pdf demo/, `expected demo intro on stderr, got: ${r.stderr}`);
+  if (r.status === EXIT.MISSING_DEP) {
+    // No backend installed: the demo explains what to install instead.
+    assert.match(r.stderr, /No PDF backend is installed/);
+    return;
+  }
+  assert.equal(r.status, 0, `demo failed: ${r.stderr}`);
+  assert.match(r.stdout, /Converted the sample DOCX to PDF/);
+});