Protect PDF

Password protect a PDF, privately

PDFMingo's Protect PDF tool adds a password to your document so only the people you choose can open it. The encryption happens entirely inside your browser using 256-bit AES, so your file and your password are never uploaded to a server, not even for a moment. Drop in your PDF, type the password twice, and the protected copy downloads with "-protected" added to the filename. There is no sign-up, no watermark and no limit beyond your own device's memory.

Real encryption, not a polite request

It is worth knowing that PDFs support two very different kinds of protection. One is a permissions flag that asks a reader not to print or copy the document. That flag is trivially ignored, because the file itself is unencrypted and any tool can simply choose not to honour it. The other is an open password, where the contents of the file are genuinely encrypted and cannot be read at all without the key. This tool does the second kind. The bytes of your document are scrambled with 256-bit AES, the same class of encryption used to protect banking and government data, and nothing in the file can be recovered without your password. Anyone who receives the file gets a password prompt before they see a single word.

Why doing it in your browser matters

Most online PDF protectors upload your document to a server, encrypt it there, and send it back. That means both your unprotected file and the password you chose passed through someone else's machine. If the document was worth protecting in the first place, that is a strange trade to make. PDFMingo encrypts the file locally: the PDF is read into your browser's memory, encrypted on your own device, and handed straight back to you as a download. We never receive the file, we never receive the password, and there is nothing on our side to leak, subpoena or breach. Close the tab and every trace is gone.

Choosing a password that is worth setting

• Length beats complexity. A four-word phrase you can remember is far harder to crack than a short password full of symbols.
• Do not reuse an important password. A PDF password often gets shared over email or chat, so it should never be a password you use anywhere else.
• Send the password separately. Emailing a protected file and its password in the same message protects nothing. Send the password by text, phone or a different app.
• Write it down somewhere safe. There is no reset link and no recovery. If the password is lost, so is the document.

What a password can and cannot do

A password controls who can open your document. It does not control what a person does once they have opened it. Someone with the password can read the file, take screenshots, copy text, print it or save an unprotected copy. That is true of every encrypted PDF, from any tool, and it is a limit of the format rather than of this page. Protection is right for keeping a salary slip, contract or medical report unreadable if it reaches the wrong inbox or a lost laptop. It is not a way to stop a trusted recipient from passing the contents on.

Opening protected files, and unlocking them later

Protected PDFs open in any reasonably modern PDF app: Acrobat Reader, Chrome, Edge, Preview on Mac, and the built-in readers on Android and iOS all prompt for the password and open the file normally. Software from before roughly 2010 may not understand 256-bit AES, so if a recipient is on something very old, warn them first. If you later want to take the password off a file you own, our Remove Password tool does that in the browser too, as long as you know the password. And if your PDF is already protected, remove the existing password before adding a new one, since an encrypted file cannot be re-encrypted while it is still locked.