Use Windows Explorer to navigate to the folder in which the file was saved. Make a copy of the auto-recover file, and make sure it does not have the same name as the original drawing. Right-click on the copy of the auto-recover file and choose "Rename." Rename the .arf file extension to .aec, and then press [Enter] to accept the new name.
If Windows is hiding your file extensions, which it does by default, you'll need to change a setting before you can rename the file extension. Click on the "Organize" button in Windows Explorer, and then select "Folder and search options." On the "View" tab, un-check "Hide extensions for known file types," and then click OK.