Hi Konstantin,
You need to maintain the Object Link first.
Step 1 :
SPRO - Document Management - Control Data - Maintain Key Fields
Maintain PMAUFK and relevant informations. I dont have IDES, may be Pete Atkin can help you on this with screenshot.
Step 2 :
SPRO - Document Management - Control Data - Maintain Screen for Object Link
Here maintain the screen number 500 as shown by Pete for Order.
Step 3 :
SPRO - Document Management - Control Data - Define Document Types
Now, you need to define here with the Object Link you have create with screen assignment.
Let us know if you still have any issues.
Regards
Terence