Put a password on a PDF before you send it, and optionally stop it being printed or copied from. The encryption is AES-256, which is what current readers expect. Everything happens on your own machine — the password you type is never sent anywhere, which is the whole point of a password.
The security engine (about 1.3 MB) loads only when you drop a file in, and it runs here rather than on a server — which matters more than usual when the file has a password on it. Your file is read on your own machine and never sent anywhere — open your browser's network tab and watch while you use it.
AES-256, the strongest of the three schemes the PDF format defines. The weak link is never the cipher, it is the password: a short or guessable one can be attacked offline by anyone holding the file, and no amount of encryption fixes that.
The open password is asked for before the file will show anything. The owner password leaves the file readable but governs printing and copying. If you leave the owner field empty we reuse your open password, because restrictions with no owner password can be stripped by any tool in seconds.
They hold in readers that honour them, which is most of them, and they are enforced properly here because an owner password is always set. Be clear-eyed though: anyone who can open and read the file can photograph the screen. Restrictions are a fence, not a vault.
No. The encryption runs inside this page, in a WebAssembly build of qpdf that downloaded to your browser. The password never leaves the tab, and there is no server here to receive it even if it wanted to.
These all work the same way — in your browser. Most are free; the ones marked as needing a plan are not.