Yes, PSPad is Windows 8 compatible. You are right, there is no version Windows 8 in list opf operating systems, cause latest full version was published before Windows 8 was released.
There is issue related to Windows 8.1 if you use WordWrap mode together with highlighting matching brackets together. -- <http://forum.pspad.com/read.php?2,62142,62143> PSPad freeware editor http://www.pspad.com
