Protect PDF Online
Add a password to a PDF online in your browser using AES-256 encryption, without uploading your file to a server.
What this tool does
NexKit PDF Tools adds password protection to a PDF using real AES-256 encryption, powered by the widely used qpdf engine compiled to run directly in your browser. Once protected, the PDF requires the password you set to be opened in any PDF viewer.
This tool encrypts an unprotected PDF. If your PDF already has a password, use Unlock PDF first, then Protect PDF again with a new password if needed.
How to add a password to a PDF
Open the Protect PDF page and upload your PDF. Enter and confirm a password, then click Protect PDF. Download the encrypted file once it is ready.
Keep the password somewhere safe - it is never stored anywhere and cannot be recovered by NexKit if lost.
Accuracy and limits
This tool supports PDFs up to 25MB and requires a password of at least 4 characters. Encryption uses AES-256, matching the strongest standard PDF encryption qpdf supports.
Privacy and file handling
Your PDF and the password you set are processed entirely in your browser. Neither is uploaded to NexKit servers by this tool.
Frequently Asked Questions
Is my file uploaded?
No. Your PDF and password are processed locally in your browser using a WebAssembly build of the qpdf engine. Nothing is uploaded to NexKit servers by this tool.
What encryption does this use?
AES-256, the strongest standard PDF encryption level supported by qpdf, the same engine used by this tool.
What if my PDF is already password protected?
Use Unlock PDF first to remove the existing password, then use Protect PDF to set a new one.
Can I recover a lost password?
No. Your password is never stored anywhere by NexKit, so it cannot be recovered if lost.