The BAK file extension is used by many different applications for backup purposes. A file with a BAK file extension is automatically created by certain programs and often just contains a copy of the original file. You can restore files of these type by replacing the ".BAK" file extension with the original extension.

The BAK file extension is used by Mozilla Firefox for backup files to replace saved bookmarks in case the original one becomes corrupted. It is automatically generated by the Firefox browser. You can see the file typically named bookmarks.bak.

The BAK file extension is used by the application RE-TOS as a data backup.

The BAK file extension is used by TBT tracker for files that contain deleted course INI file.

A software called Grade Organizer uses files with a BAK file extension for files that contain backup of user data.

The BAK file extension associated with the ACT! application contains a backup of CRM (customer relationship management) including customer information like names, addresses, and history.

The drawing software Canvas uses files with a BAK file extension as drawing backup. The backup is created intermittently until the user finishes his drawing project.

The BAK file extension is used as a backup of a T-FLEX project file. The file is created periodically until the user finishes and saves his project.

Files with .BSD file extension are found in some packages of FreeBSD and NetBSD.

The BAK file extension is associated with VoCATS (Vocational Competency Achievement Tracking System), a computer-supported system that includes course planning, lesson planning, etc. The file contains a backup of a modified test.

Various Linux operating systems use files with the BAK file extension to store some form of installation data.

The BAK file extension is associated with a number of MRDS programs. It includes the original MRDS and MAS/MILS data.

The UML (Unified Modeling Language) uses files with a BAK file extension as some sort of a backup file.

The BAK file extension is also associated with AcqURL. It contains a backup of the saved bookmarks.

The BAK file extension is associated with the Corel WordPerfect version 6.1. The file contains a backup of a WordPerfect document and is created intermittently until the user saves or finishes the project.

The BAK file extension is associated with BSL that contains a background subtraction of an image.

Files with a BAK file extension are associated with Essbase and contains a backup of the Essbase security file.

The BAK file extension is associated with the THEOS operating system and these files contain a backup of the text file os said operating system.

The BAK file extension is associated with Finale, a music writing software. It contains backup data for MUS files and is created when a MUS file is saved by the user.

The BAK file extension is associated with ProShow Gold and ProShow Producer. Files of this type stores backup of the PSH file.

Files with a BAK file extension is used by TED5 to store the backup of a level it created. These backup files are compressed by using Carmack compression.