Either the SolidWorks user doesn't know what he was doing or wanted to protect intellectual property ( I would guess the former and this file doesn't do the latter).
It should take you about 5-10 minutes to create the solid geometry.
Simply project to 2D sketches and Extrude.
Please mark this response as "Accept as Solution" if it answers your question.
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Autodesk Inventor 2013 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional
Inventor Professional 2013 SP 1.1 Edu 64-bit
GeForce GTX 560M i7-2670QM @ 2.2GHz 8GB RAM
http://home.pct.edu/~jmather/content/DSG322/inventor_surface_tutorials.htm
http://www.autodesk.com/edcommunity
Still waiting for -Draft option on any Rib feature.
