3D models from existing DXF, DWG, PDF, etc.

With the CNC coming some time in the future, I have the bright idea that I want to use it to cut out a guitar body. But since I have nearly zero artistic/design talent, I want to use existing files to create the model. It seems that PDF, DXF, DWG files are growing wild on the webs, so I have plenty to choose from. The problem I have is converting them to something useful inside sketchup, 123D design, etc. Is there an easy way, or trick to converting them? Everything I've tried just gives me a flat drawing. I did manage to find some existing 3D models, but I want to modify them in one way or another. If anyone has some tips, tricks, links to tutorials (for the artistically and design challenged) please send them my way.

And if it helps, I have Windows, Mac, and Ubuntu.

openscad can extrude from dxf files.

is that Mac or Linux?

found it