hmmm, i think i know what you're talking about and i think i know how to help, since pdo files, 3ds files, obj files, and other similar file types are only openable by certain downloadable programs such as pepakura designer, you're gonna hafta start out by finding the file you wanna open and then right click on it, chose the open with option, and the chose the select default program and then chose to browse programs, look for pepakura designer and then chose to use that and it should work well after that, by the way, once you chose to open a type of file extention it'll set that program as the default for the file extention. hope that helped, if you have any questions or any more problems, i'll be happy to help anyway i can, peace bro