No, it is not possible AFAIK. Windows relies on the file name extension to identify the file type. When you enable Settings -> Program Settings -> System Integration -> Show PSPad in context menu, you can right-click files without extension and open them via the context menu.
-- <http://forum.pspad.com/read.php?2,36560,36565> PSPad freeware editor http://www.pspad.com
