There is no editor. That file is just something that the pywright exe uses. I'm not even sure what it's for, it's a windows thing.

PyWright cases are folders in games that contain text files. Look at some of the example games to get a feel for the layout. For editing the text files, notepad.exe works fine, as does notepad++, scite, or any other text editor.

Check the help page for some links that might get you started. The gyakuten wiki page has a good intro tutorial, the documentation has some of the most important commands, and the doc.txt that comes with pywright has everything else. Docs are kind of in disarray at the moment