Pepakura Designer will open OBJ and PDO files, as well as a host of other file formats (e.g., 3DS, DAE, LWO, etc). Pepakura Viewer will only open PDO files and you cannot edit or re-scale them. Also, 4shared is not a pay site. You can have a free account with them. You just have to wait 20 seconds before you can download a file.