As you work, MicroStation saves all changes you make to the open DGN file to disk (assuming you have not turned off the default "Automatically Save Design Changes" check box in the Preferences dialog, Operation category ( File > Settings > User > Preferences ). After you close the DGN file, you can no longer undo changes with MicroStation's Undo feature. Therefore, be sure to undo any unwanted changes to the DGN file before you exit.