Put a password on a PDF
A contract before it goes out, a scan with your bank details in it, a draft you'd rather not have forwarded. Set a password to open it, choose what the reader is allowed to do with it once it's open, and get back an AES-256 encrypted file. The encryption happens in this tab.
Drop the PDF you want to lock
or choose a file
The qpdf engine (about 430 KB) is fetched only when you press the button, and it runs in this tab.
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—Blocking modification also blocks annotating and filling in forms.
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How the lock happens. The page itself is rewritten as ciphertext, and the key is derived from your password — AES-256 by default, the same thing banks and archives use. qpdf does this in the tab; the file and the password stay on your device, nothing is uploaded, and the password is never written anywhere.
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Those permission checkboxes are a request, not a guarantee. “No printing” and “no copying” in a PDF are permission bits: a convention the file asks readers to honour, not a cryptographic wall. Well-behaved readers comply; others can ignore them, and a free tool can strip them in seconds. What actually stops someone opening the file is the open password, not these checkboxes. Treat the bits as a courtesy to well-behaved software, and the password as the real lock.
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Forget it and there is no recovery. The password is not saved, not on this site, and not present in the file in any recoverable form. Close this tab and the only copy left is the one you remember.