Where are you getting the stl from? do they have a model? The model is the best thing to track down if this is not available. In toolpath, click surface before you choose rough or finish you will have a menu come up in the menu CAD FILE will be on N turn this to Y turn SURFACE to N pick your rough or finish toolpath you would like to use fill in the toolpath options when you say done it will prompt you for the stl file to use.
Hope this helps.
Steve Arteman
www.cad2cam.net
www.cad2cam.net
Programmer/ Certified Cam Instructor