PROBLEM:
A 3D linked or imported file (DWG, DGN etc) does not display as cut in section or plan views.
CAUSE:
Import category does not display cut.
SOLUTION:
Link or Import the import file in to a family with a category that cuts (Generic Model is best).
Either create a new standalone .RFA file from a template, or create an in-place family inside your project (in-place is probably easiest).
TIPS:
Although the import will cut it will not comply with the View Range of a view.
You can control layers within an import via Visibility/Graphics, the Imported Categories tab, under Imports in Families. The actual file will not be listed, but layers within it will be listed under Imports in Families.
Within the family imported files can have their View Specific Display controlled. So for example it could be made not visible in Front/Back & Left/Right views if it is 2D CAD, or not visible in Plan if a different import is used for Plan than for 3D and elevational views.
Although Imported files can be put on a subcategory the subcategory will have no effect (you can't override graphics or hide via subcategory).
Use the EXPORTTOAUTOCAD command in AutoCAD to create the 3D CAD file.