Karl, I think you'll find what is narcys_ray looking for at the middle of the video.
(Btw, Great tip , didn't know about that direct import as gdl option.)
As for the question , you have to create a new material in ArchiCAD, then give the plan texture to this material ( make sure the image dimensions are correct)
Create in the plan view a "slab" or a "plan" with the plan dimensions
Apply the new created material to this slab/plan
Adjust the placement using
Design > Align 3D Texture > Set Origin
AC12_27 |Win11_64bit|