PGP or GPG – pgp4o or gpg4o? PGP and GPG both are implementations of the OpenPGP standard whereas the GnuPG (gpg) based gpg4o is a plugin for Microsoft Outlook to encrypt and sign emails. Well of course gpg4o is able to do a lot more things around encryption. Pgp4o is just an alternative spelling used by some people whereas gpg4o is your original plugin. Nevertheless, welcome to the “right” website. Welcome to our website.