I'm not really sure what you're asking:

If you want to know how you can run external programs, the easy answer is something like this:

system("/path/to/command_name argument1 argument2") && die "Can't run 
+command: $!";
[download]

If you want to know the arguments for pgp, you should probably look at the PGP command line documentation, which I found by typing pgp 6.5.1 into google.