BAK - Backup File
This file type usually denotes it is a backup of another document or file and is often automatically created by the operating system or a program such as Autodesk’s AutoCAD. Windows may create .BAK files fo the System.INI and Win.INI as well as other modified configuration files. NOTE: In order to utilize a .BAK file, it must be renamed to the original file type. As an example, a document named “mydocument.bak” will need to be renamed to “mydocument.doc” in order to be opened properly.