I checked the file types Topsolid and Solidworks can open, and since neither can open IFC files, I think the only option here is to try to save DWG files from the 3D Window of ARCHICAD and try to open that.
The PLN file type is ARCHICAD's own file type. You should ask the architect to save a DWG file from the 3D Window. If he saves from the Floor Plan Window, only 2D will be saved, this is why he needs to save from the 3D Window.
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