PDF Lock
Add AES-256 password protection to any PDF — right in your browser. Set a user password to open the file, optionally set an owner password for permissions, and download the encrypted PDF. Everything happens on your device, so your document never leaves your computer.
Upload & Protect PDF
Drop a PDF and set your passwordsDrop a PDF here or click to browse
PDF files only. Choose file
Result
Ready when you areYour locked PDF will appear here
Upload a PDF, set a password, and click Lock PDF.
What does this PDF Lock tool do?
This tool adds AES-256 password protection to any PDF file — entirely in your browser. AES-256 is the strongest encryption standard used in PDFs today (PDF 2.0, revision 6). Once locked, the PDF will prompt for a password before it opens in any PDF reader — Adobe Acrobat, Preview, Chrome, Firefox, and all modern viewers.
The tool uses pdf-lib-encrypt, a small library that implements the ISO 32000 standard security handler on top of pdf-lib. It writes AES-256 encryption directly into the PDF's structure and validates the password on decryption, so a wrong password never silently produces a corrupted file. Everything runs locally — your PDF never leaves your device.
You can set two passwords: a user password that anyone needs to open the document, and an optional owner password that controls what the reader is allowed to do (printing, copying, modifying, annotating). If you only want to restrict actions without requiring a password to open, leave the user password empty and set an owner password.
How to password-protect a PDF
- Upload your PDF: Drag and drop a PDF into the upload zone, or click to browse your device.
- Set a user password: This is the password that will be required to open the PDF. Type it into the first field. The strength meter shows how strong it is.
- Optionally set an owner password: If you want fine control over permissions, enter a separate owner password. If you leave it empty, the user password is used for both.
- Choose permissions: Tick or untick boxes to allow or deny printing, copying, modifying, and annotating.
- Click Lock PDF & Download: The tool encrypts the PDF with AES-256 and prepares the locked file for download.
- Download: Click Download Locked PDF to save the file. Everything happens on your device — nothing is uploaded anywhere.
Why use this PDF Lock tool?
AES-256 encryption
The strongest PDF encryption standard. Compatible with Adobe Acrobat X+, Preview, Chrome, Firefox, and all modern PDF viewers.
100% private
Everything runs in your browser. Your PDF never leaves your device — no upload, no server, no logs, no tracking.
User & owner passwords
Separate passwords for opening the file and for managing permissions. Or use a single password for both.
Granular permissions
Control whether the reader can print, copy, modify, or annotate the PDF.
Fast
No queue, no waiting. Encryption happens locally in seconds — even for large PDFs.
No watermark
Your locked PDF is clean — no watermarks, no branding, no limitations.
PDF encryption at a glance
Not all PDF protection is equal. Here's a quick comparison of what's possible with this tool versus weaker or non-cryptographic alternatives.
| Feature | This tool (AES-256) | Weak 40-bit RC4 | Watermark-only |
|---|---|---|---|
| Open password required | Yes | Yes | No |
| Permission controls | Yes | Yes (weak) | No |
| Cryptographically secure | Yes | No (easily broken) | N/A |
| Modern PDF readers compatible | Yes | Yes | N/A |
| Server upload required | No | Varies | Varies |
For anything that matters — contracts, tax documents, medical records, financial reports — always use AES-256. This tool defaults to AES-256 and never falls back to a weaker algorithm.
When would you need to lock a PDF?
- Sending sensitive documents: Contracts, tax forms, medical records, or any confidential file you need to email or share.
- Protecting intellectual property: Reports, manuscripts, or research you don't want copied or redistributed.
- Restricting printing: Lock a PDF so it can be viewed on screen but not printed.
- Controlling access: Share a PDF with a client or colleague and ensure only they can open it.
- Compliance: Some industries require password protection for documents containing personal data.
- Archiving: Lock older documents so they can't be accidentally modified.
Best practices for PDF passwords
- Use a long passphrase, not a short password. A 15-character phrase like
blue-river-tiger-42is far stronger than a scrambled 8-character password. - Never reuse passwords. Use a unique passphrase for each sensitive PDF. A password manager helps.
- Store the password separately from the file. If you email the PDF and the password in the same message, anyone with access to that message can open it.
- Remember that AES-256 has no recovery. If you lose the password, the file is effectively gone. Back up passwords in a safe place before you discard the original PDF.
- Use an owner password if you want restrictions without an open prompt. You can deny printing or copying while still letting the reader open the PDF without typing a password.
- Test the locked file. Open it once in a reader you trust to make sure the password works and permissions behave as expected.