Having to do this for each and every occurrence in the Registry is extremely painful, though. I agree that any arguments passed after -z (excluding the executable path) should probably be assumed to be part of the single file argument.

But this is not an issue with PN, or even a problem with IFEO. Actually, this is because of the way the default file associations are set in Windows. Notepad doesn’t require quotes around filenames; i.e. it will consider it’s whole command line as one, single filename to open, quotes present or not. So Windows doesn’t use any for notepad, by default. Whenever you shell-run a *.txt file with the IFEO’s Debugger option set, Windows just launches the debugger and passes whatever HKCR\txtfile\shell\open\command specifies (if it’s still “txtfile” for *.txt files), and by default it is: %SystemRoot%\system32\NOTEPAD.EXE %1 (see, no quotes). Hell, long ago I made myself a context-menu shell add-in so I can open any file with notepad, and copied over the same command line.

To fix this, you (the user) would have to add quotes around notepad’s argument wherever it is used, starting with HKCR\txtfile\shell\open\command (or whatever your handler is for *.txt files). Or, the dev could implement, through a new switch, a notepad-compatible mode, where PN (after the ignored “notepad.exe”, using -z) would assume the remaining arguments of the command line is just a single file, quote or not, just like notepad.