In the FILE MENU / Under Libraries and Objects / there is a selection called OPEN GDL OBJECT... here you navigate to your DWG file and it will begin creating an Object for ArchiCAD...
When you save it... it will ask a couple of question (regular object, window, door) and where to save..
Then this object will need to be placed in your plan...
Duane
Visual Frontiers
AC25 :|: AC26 :|: AC27
:|: Enscape3.4:|:TwinMotion
DellXPS 4.7ghz i7:|: 8gb GPU 1070ti / Alienware M18 Laptop