$ pdftk MyInput.pdf input_pw PASSWORD output MyOutput.pdf
WARNING: The creator of the input PDF:
   MyInput.pdf
   has set an owner password (which is not required to handle this PDF).
   You did not supply this password. Please respect any copyright.
You can safely ignore the warning message.

Pwned Passwords
Pwned Passwords are half a billion real world passwords previously exposed in data breaches. This exposure makes them unsuitable for ongoing use as they're at much greater risk of being used to take over other accounts. They're searchable online below as well as being downloadable for use in other online system. Read more about how HIBP protects the privacy of searched passwords.

Buying a password seems crazy. But trying to make your own passwords is even crazier. C’mon – admit it, your passwords could be better. Instead of 12345 or password, your passwords could be longer, stronger, and more unique. That’s where I come in. Using a proven methodology, I build long, strong, memorable passwords using strings of words from the dictionary that I select using dice. This method has been endorsed by no less an authority than the XKCD comic

Time and time again you hear about a company having all of their users' passwords, or "password hashes", compromised, and often there's a press response including one or more prominent security researchers demonstrating how 1,000 users had the password "batman", and so on. It's surprising how often this happens considering we've had ways to do password authentication that don't expose users' passwords, or at least makes it significantly harder to crack them, for several decades.

Personally, I think it boils down to a fundamental misunderstanding about what cryptographic hash functions are and what they are—or should be—used for, and a failure on the part of security researchers and advocates, myself included, to properly explain and emphasize the differences. So here's an attempt to explain why "SHA 256-bits enterprise-grade password encryption" is only slightly better than storing passwords in plain text.