Ok, previous versions, config item "context menu" is on, target file (*.txt) is in the Associated Files list.
8.1.10 - from Windows File Explorer or Q-Dir (Quad Directory Explorer, which I think uses the same interface):
- left double click on the file, file opens a new instance of TextPad, file is opened in it
- right click on the file, context menu shows a choice of TextPad instances to open
- left double click on file opens the file in the "first" TextPad instance. Not the most recently active instance, but the first one opened.
- right click opens in context menu, opens in new TextPad instance.
Note: like other config items, I've learned: you open TextPad raw, no files, make the change, then close. Don't have T/P instances hanging around at the time. This is standard Windows behaviour. Windows actually doesn't like you opening other apps while it's thinking...