Backup files help ensure the safety of your drawing data. If a problem occurs, you can restore a drawing backup file.
Computer hardware problems, power failures or surges, user mistakes, or software problems can cause errors in a drawing. By saving your work frequently, you can ensure a minimum of lost data if your system fails for any reason. If a problem occurs, you can restore a drawing backup file.
In the Options dialog box Open and Save tab you can specify that backup files are created when you save drawings. If you do, each time you save a drawing, the previous version of your drawing is saved to a file with the same name and a .bak file extension. The backup file is located in the same folder as the drawing file.
You can revert to your backup version by renaming the .bak file in Windows Explorer to a file with a .dwg extension. You may want to copy it to a different folder to avoid overwriting your original file.