There is only one file type that uses the .PAR2 extension:
Parchive 2 Index File
Index file that contains a group of parity volumes in a Parchive 2 (PAR2) archive; may be used to recover a file archive when one of the files in the archive is lost.
The .PAR extension is used for files created with Parchive version 1.
Updated: January 10, 2008