I hunted for this in the forums and couldn't find what I needed.
Maybe I just didn't use the correct terminology.
Anyway, you know when you load a major software it asks you if you want to register all the available file types it can open?
You then can click on that file in Windows Explorer and it opens up in that particular software.
I'm not sure what to call it, file type registration seems to be the proper description.
Is there some command somewhere I've overlooked in PDN that can do this for me retroactively?