Thank you, John!

Parts of your brillant code are quite different from the the road, I thought I should take. Is it in general a bad idea using the BuiltInDocumentProperties I tried to read out? When I tried, they created errors, and you obviously avoided them ...
I think I never saw the command GetFile before, so this is (another time) a new world you're opening for me.

Thanks again, and thanks to Sam and Paul, too, for spending some thoughts on this.