How to Password-Protect a PDF (Free, AES-256)
If you're emailing a contract, an invoice, or anything with personal details, a password on the PDF is a simple, effective safeguard: only someone with the password can open it. Here's how to password-protect a PDF for free — with strong AES-256 encryption, applied entirely in your browser so the file is never uploaded.
Protect a PDF in three steps
- Open the Protect PDF tool and drop in your PDF.
- Choose a password (share it with the recipient separately — not in the same email).
- Click Protect PDF and download the encrypted copy.
Pick a good password — and share it safely
- Make it strong but memorable, or generate one with a password generator.
- Send it through a different channel than the file itself — e.g. the PDF by email, the password by text.
- Don't lose it. There's no back door; without the password the file can't be opened.
How strong is the protection?
The PDF is encrypted with AES-256, the same standard used to protect sensitive data across the industry. It can't be opened without the password. Because the encryption happens in your browser (via qpdf compiled to WebAssembly), your document never touches a server.
Need to remove a password later?
If you have the password and want an unprotected copy, the Unlock PDF tool removes it — the exact reverse of this tool, also in your browser.
Prepare the PDF first
You might want to merge several files into one before protecting it, compress it for email, or add a watermark. See all the PDF tools here.
FAQ
Is my PDF uploaded anywhere?
No — encryption runs entirely in your browser, so the file never leaves your device.
What encryption is used?
AES-256, a strong industry-standard encryption. The PDF can't be opened without the password.
What if I forget the password?
There's no recovery — keep the password safe. Anyone with it (including you) can remove it later using the Unlock PDF tool.