How can I save a part as a wavefront (.obj) file?

Hi,

I'm fairly new to Creo and am trying to export a part that I created as a .obj file. I want to import it into X-Plane's PlaneMaker. I have already managed to create a .obj file, but anytime I open it either in Creo or in PlaneMaker it is just a blank file. So far, I have been exporting the file by clicking "Save as > Wavefront (*.obj) > OK > Select Coordinate System > OK. Am I missing something? It also creates a .mtl file in the folder that I saved it in, so does that have any importance?

Thanks.