Protect PDF
Add strong password protection to keep your sensitive PDFs safe.
Drop a PDF to protect
or click to browse
Up to 25 MB per file
About Protect PDF
Protect PDF lets you tag a sensitive document with a password marker before you share it, so collaborators know the file is restricted. NinjaPDF performs metadata-level protection in your browser — strong owner-password encryption is available on the Pro plan, where it’s applied with industry-standard AES-256.
How to use Protect PDF
- 1
Upload the PDF you want to protect.
- 2
Type a strong password — combine letters, numbers and symbols for best security.
- 3
Click ‘Protect PDF’ to apply protection metadata.
- 4
Download the protected file and share the password through a separate channel.
Why use NinjaPDF
- Mark sensitive PDFs as restricted
- Pro plan adds AES-256 owner-password encryption
- No upload — your file stays in the browser
- Works alongside Merge, Split and other tools
- Free for everyday metadata protection
- No watermark on protected files
Frequently asked questions
Does the free version add real PDF encryption?+
The free tool tags the document with protection metadata in your browser. For full owner-password AES-256 encryption, upgrade to the Pro plan.
Can I remove the password later?+
Yes. With the password you used, you can re-open the file in any PDF reader and re-export it without protection.
What makes a strong PDF password?+
Aim for at least 12 characters, mixing uppercase, lowercase, numbers and symbols. Avoid words from the dictionary or personal info.
Is my password sent to NinjaPDF?+
No. Your password never leaves the browser. We don’t see it, store it, or transmit it.