Changes in EPMDocuments that have been done in Windchill only - like renaming, attributes... - are incorporated in the actual CAD files upon retrieving them in the CAD system. The WGM (or the built-in WGM in Creo) handles this.
Thus, exporting CAD models from Windchill out to the file system must use the CAD tool. So any direct download of EPMDocument primary content is not allowed in Windchill anymore.
However, when Isodraw is connected to Windchill via the WGM and is using a workspace with Creo in it, then it would be a good thing if Isodraw was able to open Creo files directly. Unfortunately PTC didn't implement this. Maybe because of the same reason as mentioned above.
In my opinion best practice working with Isodraw is using PVZ viewables instead.
