What's the use-case? If it's a one-off file to decrypt, you might be able to use GPG to decrypt it via a somewhat arcane command-line ("gpg -d foo.pdf.gpg" once you have your key set up, but I forget exactly how you do that). It actually has Mac GUI integration for email and some other stuff. They claim 10.6 and later are supported: https://gpgtools.org/
It may not work. GPG, OpenPGP, and Symantec PGP all implement the IETF PGP standard and will usually interoperate on encrypted files and emails. But there's some stuff that Symantec PGP does as proprietary extensions that GPG and OpenPGP won't handle (e.g. whole-disk encryption).
Guest, I have a big favor to ask you. We've been working very hard to establish ourselves on social media. If you like/follow our pages it would be a HUGE help to us.
SoSH on Facebook and Inside the Pylon