I don't have any experience with Hum3D, but I doubt if you can plug them directly into a 3d printer without a lot of modification. A good place to start with learning how to 3d print bodies would be the 3D Warehouse. Their digital models are free, but vary in quality from toy-like to very good. A digital body is a membrane and must be given thickness to be able to print. You do this by building a series of planes on the inside of the body. Download Sketchup and learn it. There are numerous videos and websites about it.