# Protect a PDF with a password

> Add a password to a PDF with AES-256 encryption, and optionally block printing or copying. Free, no sign-up: the file is encrypted in your browser and never uploaded.

Lock a PDF with a password so only the people you give it to can open it.

## 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

1. Drop the PDF.
2. Type a password twice, and choose whether printing and copying stay allowed.
3. 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](https://nimbopdf.com/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](https://nimbopdf.com/how-it-works/)

## 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.

## Related tools

[Unlock PDF](https://nimbopdf.com/unlock-pdf/)[Redact PDF](https://nimbopdf.com/redact-pdf/)[Sign PDF](https://nimbopdf.com/sign-pdf/)[Edit metadata](https://nimbopdf.com/edit-pdf-metadata/)

## Guides

- [How to password-protect a PDF on iPhone](https://nimbopdf.com/how-to-password-protect-a-pdf-on-iphone/)

## Sign & secure

[Edit metadata](https://nimbopdf.com/edit-pdf-metadata/)[Sign PDF](https://nimbopdf.com/sign-pdf/)[Redact PDF](https://nimbopdf.com/redact-pdf/)[Unlock PDF](https://nimbopdf.com/unlock-pdf/)[All PDF tools](https://nimbopdf.com/tools/)

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Source: https://nimbopdf.com/protect-pdf/ · Nimbo (English) · https://nimbopdf.com/llms.txt