That's pretty much what it does. And obj with make a mtl file when it is created. If Bryce doesn't understand where to find the materials, then it can give you a Bad I/O error. Just load the obj into Metal Fixer and it will "fix" whatever is wrong so that Bryce can read it. I wasn't able to import most Poser objs into Bryce until I found that. It's a wonderful tool, especially for beginners who don't feel comfortable editing their own obj or mtl files.