PDF Protect
See why browser-based PDF encryption isn't possible, and get links to free tools that can add it.
Frequently asked questions
Does clicking "Protect PDF" actually add a password to my file?
No — pdf-lib, the library this tool runs on, can't perform PDF encryption in the browser, so the downloaded file is just re-saved without any password. The tool explains this and links to free tools (SmallPDF, iLovePDF, LibreOffice) that can actually encrypt it.
Why do I need to type a password if it isn't used?
The password field only gates the "Protect PDF" button (it stays disabled until you enter something) — the text you type is never applied to or stored in the output file.
Why can't this be done entirely in the browser?
Real PDF password encryption needs to write an encryption dictionary into the file's internal structure, which pdf-lib doesn't implement client-side — that step normally needs server-side processing or a dedicated desktop tool.