What a PDF password does, and what it only asks
Locking a PDF gives you two quite different things at once. The password is real: without it the document cannot be read, by anyone, including us. The permissions beside it — printing, copying — are recorded in the file and respected by mainstream readers, which is not the same as being enforced. Knowing which is which decides what you can safely rely on.
Which tool you need
A document only certain people should be able to open
Password protect PDF. The encryption is AES-256, written as revision 6 of the PDF standard security handler, and done by the cryptography built into your browser rather than by code we wrote.
A document you want people to see but not reuse
The permissions do that as a request, and a watermark says it visibly. Neither prevents anything; between them they make the intention unmistakable.
A PDF that already has a password
It is refused rather than locked twice. Take the old password off with Unlock PDF, which needs that password, then come back and set the new one.
Everything that has to happen to the document before it is locked
Do all of it first. A locked PDF cannot be merged, split, cropped, signed or compressed here until the password is taken off again, so locking is the last step.
A password you cannot risk losing
Write it down somewhere safe before you download the file, and keep the unlocked original until you have checked that the locked copy opens.
The password is enforced; the rest is honored
Only the password controls who can open the document at all, and that part is cryptography rather than policy. Everything else is a set of flags stored in the file: mainstream readers honor them, and a reader that already has the password can choose not to.
So rely on the password for anything that matters, and treat the printing and copying settings as a statement of how you want the document handled. Reading with a screen reader stays permitted whatever else is switched off, which is deliberate.
There is nothing to reset
If the password is lost the document cannot be opened, by you or by anyone else. There is no account, nothing is uploaded and no copy of the key exists anywhere, so there is nothing anybody could reset even if they wanted to.
That is the same fact as the privacy promise, seen from the other side: a service that could recover your password would be a service that had your document. Save the password first, check the locked file opens, and keep the original until you have.
What to know before you start
- Very old software that predates the PDF 2.0 encryption scheme may not open an AES-256 file. Check it in the reader your recipient uses, as you would with any document you send.
- Nothing here can unlock a document whose password you do not have.
- Everything happens on the device you are using: the locking, the file it produces and the password you typed. None of the three is ever sent anywhere.