Protect PDF
Encrypt a PDF with a password and set what readers may do.
This tool runs entirely in your browser. Your file is never uploaded, and you can verify that in your browser's network tab. Verify it yourself: open your browser's network tab and watch. You will see one small request asking whether you have tasks left - a tool name and a hash, never the file.
What this does
Two different things are called protection, and a PDF offers both. A user password encrypts the file: without it the document cannot be opened by anyone, and that is real cryptography rather than a preference. The permission flags are not encryption at all - they record a request, such as do not print, that a well-behaved reader honours and any other reader may ignore.
Use the password before a document travels somewhere you do not control: a payslip going to a personal address, a contract sent to a counterparty, tax papers going to an adviser. Reach for the permission flags in the softer case, where a request is all you need and all you will get.
How it works
- Drop the PDF onto this page. A document that is already encrypted is refused rather than encrypted twice, because a doubly encrypted file is one no reader can open.
- Type the password people will need in order to open it. This is the field that actually encrypts; everything below it is weaker.
- Set a separate permissions password if opening the file and controlling it should be different privileges. Leave it empty and the open password is used for both.
- Choose the encryption strength, then set the toggles for printing, copying, editing, annotating and form filling.
- Press Protect PDF. The password is the only way back in, so keep it somewhere you will still have it next year.
The encryption is done by qpdf compiled to WebAssembly, running in a worker inside your browser. The password you type is used there to derive the file's key and is never transmitted - open the network tab, protect a document, and the one request you will find asks whether you have tasks left, carrying a tool name and a hash.
The two passwords do different jobs. The open password decrypts the file; the permissions password is what lets somebody lift the restrictions afterwards. qpdf needs a permissions password to set any restriction at all, so when only one box is filled in that password is used for both - one password that opens and fully controls the file.
Take the permission flags for what they are. Acrobat and most commercial readers honour them; plenty of free readers do not, and stripping them takes one pass through Unlock PDF and no password whatsoever. If a document genuinely must not be printed, the answer is not to send it.
AES 256-bit is the default because it is the strongest thing the format offers and every reader since roughly Acrobat 9 understands it. The 128-bit settings are compatibility choices for older software and are meaningfully weaker, RC4 especially. Whichever you pick, the length of your password matters more than the cipher, because the password is what gets guessed.
What this tool cannot do
- The permission flags are advisory. The encryption is real, but do not print and do not copy are requests, and any reader is free to ignore them.
- A lost open password cannot be recovered, here or anywhere else. Nothing in the file remembers it.
- An already-encrypted PDF is refused rather than encrypted a second time. Remove the existing protection with Unlock PDF first.
- The 128-bit options exist for readers too old to understand AES and are not a serious defence. AES 256-bit is the only setting worth relying on.
Questions people ask
- What is the difference between the open password and the permissions password?
- The open password encrypts the document: without it nothing can be read. The permissions password does not encrypt anything - it is what lets somebody lift the restrictions later. Fill in only the open password and it is used for both; fill in both when the person who may read the file should not be the person who may unrestrict it.
- Can someone print or copy my PDF even though I turned it off?
- Yes, if they want to. The restrictions are flags in the file, and honouring them is a convention. Acrobat and most paid readers obey; several free ones do not, and any tool that removes the owner password strips them in a second.
- Which encryption strength should I choose?
- AES 256-bit, unless you know a specific old reader has to open the file. Anything from about Acrobat 9 onwards handles it. The 128-bit options are for software older than that, and RC4 has known weaknesses. Either way a short password undoes all of them.
- I forgot the password. Can you recover it?
- No, and that is deliberate. There is no back door in the format and CekPDF does not guess passwords - building a cracker into a privacy tool would change what this site is for. If the document opens without a password and merely refuses to print, Unlock PDF fixes that instead.
- Is my password sent anywhere?
- No. Encryption runs inside your browser in a Web Worker, and the password is used there and discarded with the job. You can confirm it by opening the network tab before you press the button: one small request asks whether you have tasks left, and it carries a tool name and a hash of the bytes rather than the file or the password.
- What does the screen reader permission do?
- It controls whether assistive software may extract the text in order to read it aloud, so turning it off makes the document unusable for anybody relying on a screen reader. It stays on by default. At AES 256-bit the flag is not carried at all, so the setting only applies at a 128-bit strength.