As far as I know, you cannot open a native model in CREOview Express directly. You need a CADworker and a publishing process and convert the model into a CREOview file format. Alternative you can also create a PVZ file (CreoView file in a ZIP container). In case you have installed the GraphicAdaper on your PC, and it's implemented in your CREO installation, you can export or save directly out of CREO.
