Lock PDF
Upload a PDF, choose a password, and download a version that requires it to open.
Overview
This tool encrypts a PDF with a password using AES-256, the same standard PDF encryption every major reader (Acrobat, Preview, browser PDF viewers) already understands — the file will prompt for the password in any of them, not just here.
Encryption runs through a dedicated, widely-used PDF encryption tool server-side, since correctly implementing the PDF standard security handler isn't something safe to reinvent.
Examples
Protecting a sensitive document before emailing it
contract.pdf, password: a chosen passphrase
locked.pdf (prompts for that password to open)
How It Works
- Choose a PDF file from your device.
- Enter a password to protect it with.
- Click Lock. The file is uploaded, encrypted, and the result is returned.
- Click Download to save the password-protected PDF.
Use Cases
Emailing a sensitive document
Add a password to a contract, tax document, or personal record before sending it, so it can't be opened if it reaches the wrong inbox.
Tips
- Share the password through a different channel than the file itself (a text message rather than the same email) — a password sent alongside its file defeats the point.
- Write the password down somewhere safe. There's no recovery: if it's lost, the file is unreadable — that's what makes the encryption real.
FAQ
Yes. Encrypting a PDF correctly requires a dedicated server-side tool, so the file is uploaded, processed, and the result returned — nothing is stored, including the password.
Real encryption — AES-256, the PDF standard's own security handler. Any compliant PDF reader will refuse to open the file without the password, not just this site.
There's no way to recover it, from this tool or otherwise — that's what makes the protection genuine. Use Unlock PDF only if you still know the password.