You can try with MSWord.
if I double-click on ".PWI" file, it opens MSWord, but MSWord does not open the file. But if MSWord is already opened you can open manually the ".PWI" file (Menu File -> Open -> "InkWriter/Note Taker" (*.pwi); or simply drag and drop the file in MSWord window). Probably MSWord runs a warning that must use a plugin with security issues, but (if you know the source of file) you can answer YES then quietly open the file.
My experience is with Word 2003 only, but I suppose that it's work also with other version.
Try and good luck.