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Protect PDF with a Password

Encrypt a PDF with AES-256 so only people who know the password can open it, free and private.

Use this tool free →

NilPDF Protect encrypts a PDF with a password entirely inside your browser, using the same AES-256 standard supported by Adobe Acrobat and every major PDF reader. Type a password, confirm it, and the encrypted file downloads directly to you, nothing is ever sent anywhere to do it. If the PDF is already password-protected, enter the current password first and NilPDF will replace it with your new one. Because the encryption happens on your device and nothing is transmitted, logged, or retained, NilPDF has no way to recover a forgotten password, so keep it somewhere safe.

100% private. Your files are processed entirely inside your browser using WebAssembly. Nothing is uploaded to any server. NilPDF has no backend, there is no server to send your files to.

Frequently Asked Questions

Is protecting a PDF really free?

Yes. Completely free, unlimited use, no account required.

Are my PDF files safe when I protect them?

Your files never leave your device. All processing happens in your browser using WebAssembly (Pyodide). NilPDF has no server, there is nothing to upload to.

What encryption does NilPDF use?

AES-256, the strongest standard PDF encryption method, compatible with Adobe Acrobat and other major PDF readers.

Can NilPDF recover my password if I forget it?

No, and this isn't a limitation NilPDF can lift. The password is never sent anywhere or stored, so nobody, including NilPDF, can recover it. If you lose it, the file cannot be unlocked.

Can I change the password on a PDF that is already protected?

Yes. Enter the current password to open it, then set a new one. The new password fully replaces the old one.