“GPG for Win32” A windows port of GnuPG
I've recently been trying to synchronize my public and private PGP/GPG encryption key rings between my linux and windows machines. In doing so I've realized that the "Free" (and limited) version of "Pretty Good Privacy" (PGP) won't decrypt or create encrypted files with a .gpg extension. PGP is pretty much the standard encryption/decryption tool for personal use on Windows while "Gnu Privacy Guard" (GPG) is the standard for Linux.
So this begs the question, if you have .gpg encrypted files how do you decrypt them on a Windows machine? The answer is to use a port of GPG created for Windows. I've found a package called "GPG4Win" that includes the Win32 port of GPG and some helper tools in a bundled installer.
If you need "free" encryption on your Windows machine this could be an option for you.