The DWG format is a closed source binary file format that is not directly supported by FreeCAD. It requires an external 3rd party file converter to first convert then import the conversion into FreeCAD for use. Note that at this time, it is not possible to import 3D DWG in FreeCAD. 3D data is embedded as binary .SAT (ACIS) data, a proprietary and undocumented format.
