Documents can be encrypted with a user (aka open) password for privacy and security. A user password encrypted pdf document can be decrypted to an unencrypted pdf using:
$ pdftk d1.pdf input_pw <password> output d1_decrypted.pdf
$ qpdf --password=<password> -decrypt d1.pdf d1_decrypted.pdf
Documents might also have an owner (aka master or permissions) password.
Your donation will support ongoing availability and give you access to the PDF version of this book. Desktop Survival Guides include Data Science, GNU/Linux, and MLHub. Books available on Amazon include Data Mining with Rattle and Essentials of Data Science. Popular open source software includes rattle, wajig, and mlhub. Hosted by Togaware, a pioneer of free and open source software since 1984. Copyright © 1995-2022 Graham.Williams@togaware.com Creative Commons Attribution-ShareAlike 4.0