A RBZ file is a plugin used by SketchUp, a 3D modeling program used for computer-aided design (CAD). How to Install an RBZ SketchUp Extension · Locate the RBZ file that you downloaded. SketchUp plugins and add-ons are usually downloaded as RBZ files that must be installed. rbz file manually through SketchUp Preferences. A file extension is the characters after the last dot in a file name.