Protect PDF with a Password
Lock a PDF so that it opens only with your password. It is encrypted with AES-256 inside your browser: the file and the password never leave your device.
Letters, digits and symbols from an English keyboard, up to 127 of them.
How the lock works
The page makes a random 256-bit key and encrypts every page, picture and line of text in the PDF with it, using AES-256, the encryption PDF 2.0 sets out. The key is kept in the file, locked with your password. To unlock it, a reader has to put the password through a deliberately slow calculation first, so trying password after password takes a very long time. The document's details, such as its title and author, are encrypted too.
Choosing a password
Length matters more than anything else. Twelve characters or more, or four or five unrelated words, is far harder to guess than a short word with a digit added. Use letters, digits and symbols from an English keyboard: PDF readers turn other characters into bytes in different ways, and a file locked with one of them might not open everywhere. There is no way back without the password, so keep the original, unprotected copy somewhere safe if you might need it.
Opening the protected file
Current web browsers and PDF readers, on computers and phones, ask for the password and open it. A few older programs cannot open AES-256 files at all; that includes the PDF component built into some older Windows apps. Whoever has the password can read, print, copy and change the document, just as with the original: the password is the whole of the protection.
What it does not do
It does not offer "no printing" or "no copying" settings. Those are only requests written into the file, which a PDF reader is free to ignore, so they would promise more than they give. A digitally signed PDF loses its signature when it is protected, because the signature covers the file's exact bytes; the page tells you when a PDF is signed, before you protect it.
Frequently asked questions
What if I forget the password?
Then the file cannot be opened, by anyone, including this page. There is no back door and no reset, which is the point of the lock. Keep the original, unprotected PDF somewhere safe if you might need it again.
How strong is the protection?
The PDF is encrypted with AES-256, and the password goes through a deliberately slow calculation before it can be tried, which makes guessing slow. A short or common password can still be found by a patient computer; a long one cannot in any useful time.
Why can I not use other letters, such as Telugu, in the password?
PDF readers do not all turn such characters into the same bytes, so a file locked with them might open in one reader and not in another. Letters, digits and symbols from an English keyboard work in every reader.
Can I stop people from printing or copying it?
Not here. Those settings are only requests a PDF reader may ignore. The password itself is the real protection: without it, the file cannot be read at all.
Can I remove a password with this page?
No, this page only adds one. To take a password off, open the PDF in your reader with the password and save or print a copy without protection.
Is my PDF or my password uploaded?
No. The PDF is read and encrypted by JavaScript inside your own browser, with the browser's built-in cryptography, and the protected file is saved straight to your device. Neither the file nor the password is sent anywhere or stored - close the tab and both are gone.