A custom class must override the following functions:
virtual Acad::ErrorStatus dwgInFields(AcDbDwgFiler* filer); virtual Acad::ErrorStatus dwgOutFields(AcDbDwgFiler* filer) const; virtual Acad::ErrorStatus dxfInFields(AcDbDxfFiler* filer); virtual Acad::ErrorStatus dxfOutFields(AcDbDxfFiler* filer) const; <Destructor> (~AcDbObject)