Lock PDF
Put a password on a document without uploading the password or the PDF.
This tool runs in your browser. Your document is not uploaded. What happens to your files
How it works
- Choose one PDF.
- Enter and confirm a strong password.
- Lock the file and verify the downloaded copy opens only with that password.
Key benefit
Encryption is applied locally; the password and document are not uploaded.
Supported files and key limits
Input: PDF. Output: PDF.
Losing the password can make the document unrecoverable, and some submission portals reject encrypted PDFs.
Your password stays on your device too
Every browser tool here keeps your document out of the upload flow. This one also keeps your password there. A password sent to a server to be applied is a password that existed, in plain text, somewhere you cannot inspect. Here it is held in the page and discarded when you close the tab. The Network tab may show a small performance measurement, but it contains neither the password nor the document.
AES-256, with an AES-128 fallback
PDFOak uses AES-256 when supported and AES-128 as a compatibility fallback. AES-256 needs a 1.3 MB encryption module that loads from this site and nowhere else. If your browser cannot load it, the tool falls back to AES-128 instead of failing. The result tells you which one you got.
When PDFOak uses AES-256, it checks the finished file for an encryption dictionary before it offers the download, and falls back to AES-128 if that check fails. Either way, the file is not protected by the weak 40-bit RC4 that older software can still produce from an old PDF.
One password, and no way back
A PDF can have two passwords: a user password that gates opening the file, and an owner password that gates changing its permissions. PDFOak sets both to the one you type, so anyone who can open the file can also change it. A second password would imply a permission model that a determined reader can strip anyway.
Because neither the document nor the password is uploaded, nothing can recover a lost password. There is no reset link, no support queue and no copy on a server. That is why the form asks you to type it twice.
What a password does not do
It stops someone opening the document. It does not prove who wrote it, does not stop someone who can open it from copying the contents, and does not survive the file being printed and rescanned. If you need to show a document was not altered, that is a digital signature, not a password. Some submission portals also reject encrypted PDFs, so check before you lock a file you need to upload.
To change a password, take the old one off first with Unlock PDF, then lock the file again. This tool refuses a file it cannot read instead of guessing.