Free PDF Tool · Security

Lock PDF

Run lock pdf in your browser. Free, private, no signup — your selected files are processed in your browser and are not uploaded to our server.

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Drop your file here

or click to browse from your device

Accepts: .PDF
Important — read before encrypting: Encryption is performed by re-rendering each page as a JPEG image, then applying password protection in a freshly built PDF. The encryption is real (standard PDF password security via jsPDF), but the re-rendering process has several side effects you should know about:
  • Text selection is removed — output pages are images, so text can’t be copy-pasted.
  • OCR and searchability are lost — the original text layer is replaced by image pixels.
  • Bookmarks, table of contents, and internal links are removed.
  • Form fields and forms become non-editable — they are flattened during re-rendering.
  • File size can increase for text-heavy PDFs (images are larger than text streams).
  • Keep your password safe — there is no recovery if forgotten. PDF password security is real encryption; PDF readers should require the password to open the output.
For metadata-and-text-preserving encryption with bookmarks intact, use a desktop tool like Adobe Acrobat Pro or qpdf.

About this Lock PDF

Encrypt your PDF with a password using our lock pdf tool. Type a password (at least 4 characters) and we apply it during the PDF rebuild process. The PDF readers should require the password to open the output.

The encryption is applied via jsPDF’s setEncryption method, using standard PDF password security. PDF readers should require the password to open the output. Use a strong password; weak passwords can be guessed and there is no recovery if you forget it. Important: there is no password recovery — keep yours safe.

Your privacy is the default. Your selected files are processed in your browser and are not uploaded to our server; all processing happens client-side using PDF.js for page rendering and jsPDF for password-protected PDF output. Closing the tab clears the working session from this page; downloaded files remain on your device.

This tool is free to use with no signup required. Large files may be limited by your browser’s memory and device performance. Part of PDF Tools Base, a privacy-first collection of 161 PDF utilities. Bookmark the page for next time, and explore related tools in the footer below.

How to use the Lock PDF tool

  1. Drop your PDF file.
  2. Type a password (at least 4 characters).
  3. Click Process to encrypt.
  4. Download the password-protected PDF.

Why use PDF Tools Base?

100% Browser-Based

Lock PDF processes selected files in your browser. Your selected files are processed in your browser and are not uploaded to our server.

No Server Upload, No Signup

Your selected files are processed locally in your browser. No account, no server upload, no email needed.

No Watermark Ever

Outputs are clean. We never stamp our brand or a paywall watermark on your files.

Free to Use

No accounts and no signup. Use the tool as much as you need within reasonable browser limits.

Works on Every Device

Windows, Mac, Linux, iPhone, iPad, Android, Chromebook. Any modern browser.

Built on Open Source

Powered by PDF.js and jsPDF for browser-side password protection.

Common uses for lock pdf

Confidential contracts

Open only to those who know the password.

Financial reports

Share with auditors but no one else.

Personal records

Protect tax docs before emailing.

HR documents

Salary letters, NDAs, internal memos.

Frequently asked questions

Is Lock PDF safe to use?

Yes. Everything happens in your browser. Your selected files are processed in your browser and are not uploaded to our server. Closing the tab clears the working session from this page; downloaded outputs remain on your device until you delete them.

Do I need to register or sign in?

No. No account, no email, no sign-up. Open the page and start using the tool immediately. Free to use, no signup needed.

Is there a watermark on the output?

No. PDF Tools Base never adds a watermark or branding to your output. Your final file is clean — just what you produced from the original.

Is there a file size limit?

Phones may struggle with PDFs over 50–100MB; desktops may handle larger PDFs but can still fail on very large or complex files. Large PDFs may be slow or fail depending on browser memory, page count, encryption type, and PDF complexity.

Does this work on mobile devices?

Yes. The tool works on all modern mobile browsers: Chrome on Android, Safari on iOS, Firefox, Edge, Brave. The drag-and-drop also accepts files from your phone’s file manager.

What if I forget the password?

There is no recovery if you forget it. PDF readers should require the password to open the output. Use a strong password and verify the downloaded PDF in your target viewer. Weak passwords can be guessed.