pspshellx64.dll is context menu extension - right mouse possibility to open file with PSPad. It's registered library - this is a reason, why you can't remove it. Run PSPad, go to menu settings / System integration and disable integration in explorer or choose registry way and close PSPad. This should unregister this file.
Or you can do it manually: open command line window regsvr32 /u "c:\program files (x86)\pspad editor\pspshellx64.dll" -- <http://forum.pspad.com/read.php?2,64033,64037> PSPad freeware editor http://www.pspad.com
