Protect a PDF with a password (AES-256)

The file is encrypted with AES-256, the strongest method the PDF format has (PDF 2.0's), which every current reader opens. The password matters more than the method: a short or common one can be guessed by someone with the file, so use eight characters or more and not your name or birthday.

No. The file is locked by qpdf, a free PDF tool that downloads to your browser from this site when you choose the file, and runs there. The passwords are used in this tab only — they are not sent anywhere, not saved and not logged. The only thing we are told is that a run happened.

Under More options you can let someone with the password read the file but not print it, copy its text and pictures, or change it. Adobe Reader, browsers and phone readers respect these switches, but not every program does, so they are a request rather than a lock. A permissions password, if you set one, opens the file with everything allowed.

No, and nobody else can either — that is the point of the lock, and the password never reaches us. Keep your original, unprotected file, and keep the password somewhere safe.

No mark is drawn on any page, and the pages are exactly as they were. The file's metadata records that it was made at filedone.ai with no AI involved, under a provenance id; that one label is left readable without the password, and nothing in it is about you or the document. A PDF that already needs a password must be unlocked first; one with restrictions only gets your new settings instead.