I have one problem.
How can I create file with extension 17?

Because I trying to change DutyFree Shop (DF Shop).
Files with ext. 17 are in red rectangle.
If I change picture in DF Shop, file with same name and extension 17 will have about 100 B and I will not see the picture in the game. Why? example in green rectangle.
Sorry for my English and Deutsch.
I can't speak Deutsch.
edit: I used GLJ and GLI packer and unpacker for extracting GLI files from Airline Tycoon.