From:  jbshorty
only problem to use SU is that it imports only polygons. So don't expect accurate measurements except for planar surfaces which are also parallel. Otherwise, you can not be sure to get accurate snapping for centers, radius/diameter, quads, midpoints, etc... if i were trying to find a free solution, i would use Rhino's printing directly to PDF with vector output... Or you could also use Alibre's free version