PSPad doesn't store settings into registry. There are 2 files: %AppData%\PSpad\PSPad.ini - user config (for portable is stored in application folder) application folder\PSPad_MU.ini - PSpad global settings
System integration using DLL require admin rights to register DLL (COM object) This can be done by installer or running PSPad with elevated rights -- <https://forum.pspad.com/read.php?4,71034,71037> PSPad freeware editor https://www.pspad.com
