Yes. If you have a purchased key for pep designer, you can export the model as an .obj. Just click "File" then "Export" then "3D Model/UV Info (*.OBJ)." Now, be careful, if you are getting ready to edit someone else's work, make sure you have thier permission to do so. I know a lot of modelers that would rather you not edit thier models, unless it is for personal use and you don't plan on sharing it.
and to add, if they had things in multiple layers, then turned that into pdo. If you try to convert back, it turns it all into 1 layer rather than the multiple ones.