Your question makes no sense. You said you've written a WPF app and you''re trying to launch and .EXE. OK, you can do that with the Process class
Then you mention a WCF service and you're trying to launch "that .EXE" from that? What .EXE are you talking about? Where is the WCF service hosted? What .EXE are you trying to launch? Are you trying to launch "that .EXE" on the same machine as the WCF service?
If you're trying to run a WCF service, it MUST be hosted, either by IIS or by self-hosting. You have no other options.