About Protect PDF / Add Password
This tool locks a PDF with a password using real AES-256 encryption, the same strength used to protect classified government information — once protected, the file cannot be opened by anyone who doesn't know the password, in any PDF reader, on any device. Optionally, you can also block printing and copying even for people who do have the password. All encryption happens locally in your browser using a genuine, battle-tested PDF encryption engine (QPDF, compiled to WebAssembly); your file and password are never uploaded to a server.
About the Encryption This Tool Uses
Not all "password protect PDF" tools are equally secure — some older or simpler tools still use a decades-old scheme called RC4 with a 40-bit key, which modern computers can crack in minutes and offers little real protection. This tool instead uses AES-256, the current, modern PDF encryption standard, via QPDF, a mature, open-source PDF library used throughout the industry. With a reasonably long, unique password, this provides genuine protection against unauthorized access. That said, encryption strength only matters as much as the password itself — a short or common password is still comparatively easy to guess regardless of the algorithm behind it, so choose something long and hard to guess, and store it somewhere safe. If you lose it, there is no backdoor or recovery method — the file becomes permanently inaccessible.
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