The following information briefly describes the types of files you are most likely to encounter when you purchase Poser content.
BUM files: Bump map files (companion textures that give some content a bumpy appearance) that are required for older versions of Poser. Since the Poser 4 render engine has been removed, BUM files are not supported fully in Poser 8. You can use them in the Gradient Bump channel in the Material Room, but the result is not that noticeable. I would suggest using a different file format if you are going to use an image to create your bump maps.
CM2 (CMZ when compressed): Camera files that are installed and saved into the Runtime\Libraries\Cameras folder and found in the Cameras Library.