Click a DGN underlay and right-click in the drawing area. On
the shortcut menu, click DGN Clip.
At the command prompt, enter n (New
Boundary).
Enter p (Polygonal) or r (Rectangular), and then draw the boundary on the
underlay.
If you are
drawing a polygonal boundary, you are prompted to specify
consecutive vertices. To finish drawing a polygon, press ENTER or
right-click anywhere in the drawing area.