Protect a PDF with a password, free and in your browser

Drop a PDF here

or paste with ⌘V · up to 400 MB per file · stays on your device

Key facts

Price: Free, no sign-up, no watermark
Upload: Never: the file is processed on your device
Works on: Any recent browser on a computer, iPhone, iPad or Android
Files: Up to 400 MB per PDF on a computer, 150 MB on iPhone and iPad. Larger files depend on your device's memory.
Updated: October 4, 2026

Nimbo encrypts the whole document with AES-256, the strongest encryption the PDF format supports: without the password, the pages can't be opened in any reader. You can also stop printing or copying; standard readers respect those restrictions. Everything happens in this tab, so neither the file nor the password leaves your device.

How it works

Drop the PDF.
Type a password twice, and choose whether printing and copying stay allowed.
Select Protect PDF and download the protected file.

Supported files

Input: one PDF without a password. Output: one PDF encrypted with AES-256.

Up to 400 MB per PDF on a computer, 150 MB on iPhone and iPad. Larger files depend on your device's memory.

When to use it

Send a contract, payslip or medical document by email without exposing it.
Share a PDF on a shared drive where only some people should read it.
Archive sensitive scans behind a password.

Quality and limitations

If you forget the password, the PDF can't be recovered: keep your original.
Printing and copying restrictions depend on the reader respecting them; the password is what really protects the content.
Very old readers (from before 2009) can't open AES-256 files.

Common issues

“This PDF already has a password.”: Unlock it first with Unlock PDF, then protect it again with the new password.
The recipient can't open the file.: Check that they use a recent reader (Preview, Acrobat Reader, any browser) and type the password exactly, capitals included.

Private by design

This tool runs entirely in your browser with JavaScript. Your file is read and processed on your device and is never uploaded to a server. Closing the tab discards everything.

See how it works, step by step

Frequently asked questions

How secure is the protection?

The file is encrypted with AES-256. Its strength then depends on your password: use at least 10 characters, mixing words, numbers and symbols.

Is my PDF or my password uploaded?

No. Both stay in your browser; the encryption happens on your device.

Can I remove the password later?

Yes, with Unlock PDF, as long as you know the password.