Files that contain the .set file extension can be associated with Microsoft's Backup File Set. The SET file contains the set of files that a user wants to back up. When you back up additional files, the new files are also are added to the SET file archive.
The .set file extension is also used by a number of applications to store the user's application configuration settings and preferences. The file is loaded by the application when the program is run on the system. Some of the applications that commonly use the SET file format for this purpose include Diablo II, AutoCad and Corel Painter.
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If you have additional information about the SET file format or software that uses files with the SET suffix, please do get in touch - we would love hearing from you.