Lock PDF, Add a Password
Protect a PDF with strong AES-256 encryption, free, and 100% in your browser. Your file is never uploaded.
100% private, your PDF is processed in your browser and never uploaded.
How to password-protect a PDF
Adding a password to a PDF is the simplest way to keep a sensitive document private when you email it, share it on a drive, or store it in the cloud. Contracts, invoices, ID documents, medical reports, salary slips and financial statements all benefit from a password so that only the intended recipient can open them. This tool locks any PDF with strong encryption in a couple of clicks.
Drop your PDF above, type a password, confirm it, and click Add password. The file is encrypted locally and you can download the protected copy immediately. From then on, anyone who opens it, including you, will be prompted for the password.
AES-256: real, modern encryption
We protect your PDF with AES-256, the strongest encryption the PDF format supports and the same standard used by banks and governments. Many older "lock PDF" tools still use RC4, which is considered weak by today's standards. Under the hood this tool uses a WebAssembly build of the trusted open-source qpdf engine, so you get proper, standards-compliant encryption, not a flimsy "view restriction" that any reader can bypass.
Why lock a PDF in your browser?
The whole reason you're encrypting a document is to keep it confidential, so uploading it to a stranger's server first makes no sense. This tool never uploads your file. The PDF and the password you choose stay on your device; the encryption happens inside your browser tab and the protected file is generated locally. Nothing is stored or logged, and you can verify there's no upload in your browser's network inspector.
Choosing a strong password
Your document is only as secure as the password you pick. Use at least 8 to 12 characters with a mix of letters, numbers and symbols, avoid names and dates, and don't reuse a password you use elsewhere. Crucially, store the password somewhere safe: PDF encryption is genuinely strong, which means a forgotten password cannot be recovered, the document would be lost.
What's preserved
Locking a PDF is lossless. Your text stays selectable, images stay sharp, form fields keep working, and any digital signatures remain valid. Changed your mind, or received a locked file you want to open freely? Use Unlock PDF to remove a password you know. Need to verify a signed document instead? Try our PDF signature validator.
Lock PDF, frequently asked questions
How do I password-protect a PDF?+
Drop your PDF above, choose a password, confirm it, and click Add password. The tool encrypts the file with AES-256 in your browser and gives you a protected copy to download. Anyone who opens it will be asked for the password.
What encryption is used?+
AES-256, the strongest encryption supported by the PDF standard and the same algorithm used to protect banking and government documents. It is far stronger than the older RC4 scheme used by many legacy tools.
Is it safe to encrypt sensitive PDFs here?+
Yes. Encryption runs entirely inside your browser using WebAssembly. Your PDF and your chosen password are never uploaded, stored, or logged, so confidential contracts and statements stay private.
Will I be able to remove the password later?+
Yes. As long as you remember the password, you can remove it anytime with our Unlock PDF tool. Keep your password somewhere safe, if you forget it, the document cannot be recovered.
Does encrypting change the PDF's content?+
No. Encryption is lossless, text, images, layout, form fields and digital signatures are all preserved. Only a password requirement is added.