creo Illustrate is not used for 2D-illustrating. It's "only" for "managing" existing 3D models that they are suitable for an ET-catalogue or a user manual. You can then export them in various formats. But: You cannot for example draw any elements in creo illustrate.
IsoDraw is for creating 2D graphics in perspective. You can import 3D models and convert them (after adjustment) into 2D. And then further process.