I understand. There are 2 requests what goes against itself: 1. admin needs to have clear install (even own) without touching it by users 2. admin wants users let change installation (your case)
Your situation is soluble by installing PSPad out of Program files folder (as you suggested) or setting write rights into Program Files\PSpad folder (and child objects) for users -- <https://forum.pspad.com/read.php?2,78375,78378> PSPad freeware editor https://www.pspad.com
