Steps:
- Go and click on the Application menu (The big Red A or the Red Diamond symbol in 2019)
- Click on Option
- Go to open and save tab on Option dialog box and click on AutoCAD 2010 Drawing (*dwg) drop down to select AutoCAD 2007 Drawing (*dwg)
Note: Any of your save design now save as 2007 version so that a user of AutoCAD 2007 can view your design but when you leave at 2010 you restricted 2007-2009 users from viewing your design.