The File Extensions Database

.BAK File Extension

  • Developer by: Mozilla
  • Category: Backup Files

What is an .BAK file?

.BAK is Firefox Bookmarks Backup

A BAK file is a backup of the Firefox bookmarks file, which can be used to replace saved bookmarks in case the main bookmarks file becomes corrupted. It is automatically generated by the Firefox web browser and typically named "bookmarks.bak".

The bookmarks.bak file is located in the following directories on Windows and Macintosh systems:

  • Windows -
    C:\Documents and Settings\UserName\Application Data\MozillaFirefox\Profiles\[random-name]
  • Mac -
    /Users/[username]/Library/Application Support/Firefox/Profiles/[random-name].default
Programs that open Firefox Bookmarks Backup
Mozilla Firefox
Mozilla Firefox
File Type 2 Backup File
Category: Backup Files Format: Text and Binary

A BAK file is a backup of another document or file, commonly created automatically by software programs or by the operating system. The file most often just contains a copy of the original file and can be restored to the original by replacing the ".bak" extension with the original extension.

Often BAK files are created by simply appending ".bak" to the original filename. For example, document.doc may have a backup file document.doc.bak.

NOTE: An example program that uses the ".bak" extension is AutoCAD. Windows may also create BAK files for the System.ini and Win.ini files.

Programs that open Backup File
Autodesk AutoCAD 2018
Microsoft SQL Server 2016
File Type 3 ACT! Backup File
Developer by: The Sage Group Category: Backup Files Format: Binary

Backup file created by ACT!, an application used for customer relationship management (CRM); contains a backup of CRM data, which includes customer information such as names, address information, and history.

ACT! BAK files are used for restoring data in the event the CRM data is lost. They are usually created on a periodic basis and when upgrading ACT! software.

NOTE: Sage ACT! became Swiftpage Act! in 2013.

Programs that open ACT! Backup File
Swiftpage Act!
File Type 4 MobileTrans Backup File
Developer by: Wondershare Category: Backup Files

A BAK file is a backup file created by Wondershare MobileTrans, a program used to backup and transfer data from and to devices. It contains data backed up from a device, such as contacts, messages, calendar information, call logs, photos, music, videos, apps, and app data.

BAK files are the primary file type associated with MobileTrans. The file is created when backing up a phone to a computer. To do this in MobileTrans, click "Back Up Your Phone" on the homepage of the program, select the content to backup, and click "Start Transfer". The BAK file will then be created to store the backup data and placed in the following directory:


To restore a BAK file to a device in MobileTrans, click "Restore From Backups" on the homepage of the program, click "MobileTrans", select the BAK file you want to restore, and click "Start Transfer".

Common BAK Filenames

[name of device]_[date]_[time].bak - Naming convention for BAK files created by MobileTrans.

Programs that open MobileTrans Backup File
Wondershare MobileTrans
Wondershare MobileTrans
File Type 5 Finale Backup File
Developer by: MakeMusic Category: Backup Files

File created by Finale, a music notation application for playing instruments, vocals, etc.; replaced by the .BAKX file, which was released in Finale 2014; contains backup data for .MUS files; created when MUS files are saved by the user.

To create a BAK file:

  • You must first enable the backup creation option.
  • Select Finale [version] → Preferences....
  • Select "Save and Print" in the list on the left of the "Preferences" window, check the "Make Backups When Saving Files" checkbox, and click OK.
  • Now when you save your MUS file, a BAK file will be created.
  • Programs that open Finale Backup File
    MakeMusic Finale
    MakeMusic Finale

    How to solve problems with BAK files

    • Associate the BAK file extension with the correct application. On :
      Windows: Right click on any BAK file and then click "Open with" > "Choose another app". Now select another program and check the box "Always use this app to open *.BAK files". Mac: Right click (or Ctrl-click) the BAK file, then click "Open with" > "Other...". Then choose another program and check the "Always Open With" box. Linux: Right click on the file, and select "Open with" and choose another program. iPhone: Tap the file. If you do not see an app to open the file, then tap Share "Share" and choose an app. Alternatively, save the file. Then open the Files app Files app. There long-press on the file, then release your finger. You will see a black menu bar. Then tap "Share" and select an app. Android: Tap the Settings icon on your smartphone, then tap on the Apps section. There tap the Options icon in the top right-hand corner of the screen to change the default apps.
    • Update your software that should actually open .BAK is Firefox Bookmarks Backup. Because only the current version supports the latest BAK file format. Search, therefore, e.g. on the Mozilla manufacturer website after an available .BAK is Firefox Bookmarks Backup update.
    • To make sure that your BAK file is not corrupted or virus-infected, get the file again and scan it with antivirus software.