Appendix C File Extensions File extensions are the bane of the computer user's existence. They number in the many hundreds (AutoCAD alone claims nearly 200) and even if you pare the list down to a useful few, it's still quite a collection. Here we will focus on those extensions that are important to an AutoCAD user, as chances are you will encounter most, if not all of them while learning the software top to bottom. They will be listed alphabetically (with explanations and/or descriptions), but grouped in categories so as to bring some order to the chaos and prioritize what you really need to know and what you can just glance over. After AutoCAD's list there is a further listing of extensions from other popular and often-used software, which you may find useful if you are not already familiar with most of them. AutoCAD Primary Extensions · .BAK (BAcKup file) BAK is an AutoCAD backup file that is created and updated every time you save a drawing, provided that setting is turned on in the Options dialog box. The BAK file is the same name as the main DWG file, generally sits right next to it, and can be easily renamed to a valid DWG if the original DWG is lost. · .DWF (Design Web Format file) DWG is a format for viewing drawings on-line or with a DWF viewer. The idea here is to share files with others that don't have AutoCAD in a way that enables them to look but not modify. If this sounds like Adobe PDF, you are correct; DWF is a competing format. · .DWG (DraWinG file format) DWG is AutoCAD's famous file extension for all drawing files. This format can be read by many of Autodesk's other software products as well as by some competitors. The format itself changes somewhat from release to