PDF passwords explained

The open password

Also called the user password or document open password. Without it, the PDF can't be opened at all: the contents are encrypted, and the password is the key. This is real protection, as strong as the encryption and the password chosen.

The permissions password

Also called the owner password. A PDF can open without any password but still ask readers not to allow printing, copying text or editing. The permissions password is needed to change those settings.

These restrictions are honoured by well-behaved PDF readers, but they aren't strong protection: anyone who can open the document can read it, photograph it or retype it. Use them as a polite "please don't", and use an open password when the content itself must stay private.

Which encryption to use

PDFs have used several encryption methods over the years. Old 40-bit and 128-bit RC4 encryption can be broken with ordinary tools and shouldn't be used for anything sensitive. AES-256, supported by every current PDF reader, is the standard to use. PDF Workdesk's Protect PDF always uses AES-256.

Choosing a password that holds

• Strong encryption only helps with a strong password: a short or guessable one can be tried by software millions of times a second.
• Use four or more random words, or 12+ characters mixing letters, numbers and symbols.
• Don't use a date of birth or a name if the recipient's details are known to others.
• Send the password a different way from the document, for example by text message when the PDF goes by email.
• Keep a copy of the password. With proper encryption there's no recovery: not even the tool that created it can open the file.

Removing a password

If you know the password and want a copy that opens without it, for filing, merging or uploading, Unlock PDF removes it in your browser. Neither we nor any honest tool can remove a password you don't know.