Hallo Mathias,
thank you for your answer. Yes I tried it: I first pressed the Ctr/Shift key and then clicked and dragged the file and then it didn't work. After reading your post I tried again and found out that I have to first klick the file and then press the Ctrl/Shift key. If I do it in this order, it works fine. However, I would appreciate if both worked!
Best regards - Ulrich