PGP Encryption Desktop does not start automatically with Windows.
The Encryption Desktop PGPtray.exe is not a Windows service, but is part of the Windows StartUp applications. A shortcut to it is found in "C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp"
If the PGPtray isn't launching, it is possible the existing shortcut is corrupt. Create a new one from "C:\Program Files (x86)\PGP Corporation\PGP Desktop" on 64-bit systems, or "C:\Program Files\PGP Corporation\PGP Desktop" on 32-bit systems, by right-clicking the PGPtray.exe file and choosing to Create Shortcut, then move that shortcut into the StartUp folder. Windows requires Administrator rights to do this. The old shortcut can be removed.
Another possible reason of blocking PGPtray.exe to run is a pending Cumulative Windows Update. As soon as it is properly installed, issue gets resolved after a reboot.