You can use the CAD-drawing as a background image in the 3D view. Usually it is recommended to use the option Represent 2D projection of dwg / dxf in 3D view from the Property Page.
Fig. 399 Using 2D projection of dwg / dxf in 3D view
Fig. 400 3D view with DXF background
You can display or hide the dwg / dxf background from the Window toolbar.
