Open files in separate windows?

Sorry to ask stupid questions, but...

I have had PSPad running on my home computer for years and I have it configured so that when multiple files are being edited, each is within its own window (inside the one PSPad window). I just got a new computer at work, installed PSPad, and copied the settings from my home machine to the new work machine. However, on the work machine, each file is in a tab and not separate windows. What configuration setting have I missed???

Program settings / system
Uncheck option Use only one programm instance

Thank you. One issue: I found the setting you mentioned, but there is a red square next to it and it is grayed out. Why?

Red sign means you need to run PSPad as admin to have access to some options, see the explanation in the left bottom corner.
After setting you can start pspad normally again

Thank you. I did that, but still no individual windows...

Fike open inside PSPad are open inside PSPad instancw. Files open outside PSPad are open in separate PSPad instances