I’m still investigating the first one, but it doesn’t work right now (and it won’t work in any of the WinForms versions either). Vaguely, this requires the app to be able to handle startup parameters so that you could run the app from the command line and pass it the name of a file to open. (Something like .NETpad C:\Users\paul\Desktop\textfile.txt.) This is curiously difficult in WPF, but I’m working on it.
I have, however, figured out drag-and-drop, by which I mean the ability to drag a text file onto the application and have it open that file. So let’s take a look at that, and at Visual Studio’s very limited WPF application publishing capabilities.