Protect PDF adds an open password to a PDF and encrypts it with AES-256. Anyone who receives the file needs that password to see the pages. You can also decide what readers may do once it is open: print it, copy text and images, change the content, or add comments and fill forms. The output is a new file named after the original, with -protected on the end.
The encryption runs inside your browser with JavaScript. Neither the PDF nor the password leaves your device, so there is nothing for anyone to intercept and nothing stored once you close the tab. That also means the password cannot be reset or recovered: if you forget it, the protected file cannot be opened again, so keep the original copy somewhere safe. Files up to 100 MB, one at a time.
Two things to know. AES-256 is a newer standard than some PDF software supports: Acrobat 9 or later and current browsers open these files, but very old viewers will not. And the permission settings are a request to the reading software rather than a hard lock. Most viewers honor them, some ignore them, and anyone who knows the owner password can remove them, so rely on the open password for anything that truly needs to stay private.
How to use Protect PDF
- 1Select the PDF, or drop it onto the page. The tool protects one file at a time.
- 2Type a password of at least four characters in the Password field, then type it again under Confirm password. The Protect PDF button stays disabled until the two match.
- 3Optionally fill in Owner password (optional), a separate password that bypasses the restrictions below. Leave it blank to reuse the open password for both.
- 4Under What readers may do, check or uncheck Print the document, Copy text and images, Change the content, and Add comments and fill forms. Printing and copying are allowed by default; changing and commenting are not.
- 5Click Protect PDF and download the file, which ends in -protected.pdf.
Frequently asked questions
- How strong is the encryption?
- The file is encrypted with 256-bit AES, the encryption method defined in the current PDF standard. The weak point is the password itself: the tool only requires four characters, but a short or guessable password can be found by trying possibilities, so use a long one for anything sensitive.
- Is my password or file sent to a server?
- No. The encryption runs entirely in your browser with JavaScript. The PDF and the password stay on your device, and FreeAIPDF never sees either of them.
- What happens if I forget the password?
- There is no way to recover or reset it, because nothing about the file was ever stored anywhere. The Unlock PDF tool removes a password you already know; it cannot break one you have lost. Keep an unprotected copy of the original in a safe place.
- What is the owner password for?
- It is a second password that opens the file with full rights, ignoring the print, copy and edit restrictions. If you leave it blank, the open password is used for both, which means anyone who can open the file can also remove the restrictions with a tool like Unlock PDF.
- Can I stop people from copying or printing my PDF?
- You can ask. Unchecking Print the document or Copy text and images sets flags in the file that most PDF viewers respect, but the PDF standard treats them as permissions rather than encryption, and some software ignores them. Note that blocking copying also blocks text extraction by screen readers in viewers that enforce it.
- Why will the protected file not open in my PDF viewer?
- AES-256 encryption needs Acrobat or Adobe Reader 9 or later, and some older or lightweight viewers do not support it at all. Current browsers and up-to-date desktop viewers open these files normally, so if yours does not, try opening the file in a browser or a recent version of Acrobat Reader.