I'm making a note about this here mainly to refresh my own memory later, when
I find myself needing to create a decrypted version of a PDF that I have
the damn password for:
pdftk is a handy little program
which very neatly takes a password and PDF as input, and can produce an
unencrypted version (with or without any of the permissions changed) as output.
I can't believe I spent all night searching for something like this (and
started looking at
Ghostscript
hackery as possible solutions) and never came across it. My
Google-fu is weak. :-P