There are several PGP SDKs and wrappers available. I used freeware nsdppgp3.dll wrapper with FoxPro applications like COM object instantiated through CreateObject function:

oPgp = CreateObject("Nsdpgp3Lib.PGP")

For your PGP SDK, which btw may have COM interface too, try to find VB examples -- the closest thing to VFP. Almost always can be perfectly translated to VFP code.

If you have Dependency Walker or similar software installed, check what's inside that dll. You will see whether there are regular functions exposed or it has COM interface: DllCanUnloadNow, DllGetClassObject, DllRegisterServer, DllUnregisterServer.