Feature request: open launched files in most recent instance

I have several file types associated with PSPad to open directly from Windows Explorer. This is fine in single-isntance mode, but in multiple-instance mode, it will open a new instance for every file.

Would it be possible to have an option to force the file to open in the most recently-used instance of PSPad? Or, perhaps, the ability to set one particular instance as the "primary" instance?

Yes. Disable multiinstance.
when you want new instance, start PSpad with /N parameter. All files will open in main instance.

Woah... perfect! Thank-you!