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.BAK file extension

To open .BAK files on Windows, check the filename and folder for clues, such as .dwg.bak, .txt.bak, a SQL Server backup folder, or an application-specific backup directory.

To open a .BAK file, first identify the application or original file it was backed up from, then open or restore it with that application. Do not assume every .BAK file works the same way; the extension usually means “backup copy,” not a universal data format.

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Last updated: April 29, 2026 · Reviewed by Julian Stricker

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .BAK files

Use these platform-specific instructions to open .BAK files safely.

Windows

  1. Check the filename and folder for clues, such as .dwg.bak, .txt.bak, a SQL Server backup folder, or an application-specific backup directory.
  2. If it is a SQL Server backup, restore it using Microsoft SQL Server restore tools rather than double-clicking the file.
  3. If it is an AutoCAD drawing backup, make a copy, rename the copy from .bak to .dwg, and open it in AutoCAD.
  4. If it appears to be a text or configuration backup, right-click it, choose Open with, and try a trusted text editor such as Notepad or another editor.
Full Windows guide

Mac

  1. Control-click the file, choose Get Info, and inspect the full filename to see whether it is a backup of a known file type, such as .txt.bak or .dwg.bak.
  2. If it is a backup of a normal document, duplicate the file first, remove the .bak suffix from the copy, and open the copy with the original application.
  3. If the file is plain text, Control-click it, choose Open With, and select a text editor.
  4. For database or CAD backups, use the appropriate desktop application or transfer the file to a system where that application is available.
Full Mac guide

Linux

  1. Use the file manager or the file command to inspect the .bak file; Linux shared-mime-info may classify it as a generic backup file rather than identifying the real contents.
  2. If it is a text/configuration backup, open it with a text editor.
  3. If it is a backup of a known file type, copy it first, restore the original extension on the copy, and open it with the matching application.
  4. For SQL Server, CAD, or other application-specific backups, restore or open the file using the software that created it.
Full Linux guide

iOS

  1. The Files app may preview simple text .bak files, but iOS has no universal .BAK opener; if preview fails, transfer the file to a desktop system and open it with the application that created it.
  2. Do not rename and open the only copy; duplicate it first if you need to restore the original extension.
Full iOS guide

Android

  1. Android has no universal .BAK opener; a simple text backup may open in a text editor, but database, CAD, and application backups usually need the original desktop software.
  2. If you do not know the source application, transfer the file to a Windows, macOS, or Linux computer for inspection before renaming or restoring it.
Full Android guide

Security notes

  • .BAK files can contain sensitive data, including full databases, drawings, configuration files, browser data, or personal documents; treat them as confidential backups.
  • Do not upload an unknown .BAK file to an online converter or viewer unless you are sure it contains no private or regulated data.
  • Do not rename an unknown .BAK file to another extension and run it. The .bak suffix does not prove the content is harmless.
  • When restoring database backups, restore to a controlled test environment first if the source is untrusted or unknown, to avoid overwriting data or exposing sensitive contents.

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Can't open this file?

These are the most common causes and fixes when .BAK files fail to open.

Common reasons

  • The .BAK file does not open when double-clicked
  • SQL Server .BAK opens as unreadable data
  • AutoCAD drawing backup will not open
  • The restored file is corrupt or incomplete

Fix steps

  1. Look at the filename, folder, and related files to identify the original application or original extension.
  2. Try opening a copy with the program that created the backup.
  3. If the file is small and likely text-based, inspect it with a text editor.

OS-specific troubleshooting

What is a .BAK file?

A .BAK file is commonly a backup copy created by software, users, or automated save processes. The file contents can vary widely: it may be a SQL Server database backup, an AutoCAD drawing backup, a renamed copy of a text/configuration file, or a backup used by another application. On Linux desktops using shared-mime-info, .bak may be classified as application/x-trash for “backup file,” but this is not an IANA-registered media type.

Background

.BAK is one of the most common generic backup extensions. Many programs create backup copies by appending or replacing the original extension with .bak, so a file such as document.txt.bak may simply be an older copy of document.txt. In those cases, the safest approach is to duplicate the .bak file, restore the original extension on the copy, and open it with the same program that normally opens that file type.

Some .BAK files are application-specific backups. Microsoft SQL Server documentation recommends using the .BAK extension for database backup files, which are restored through SQL Server tools rather than opened like ordinary documents. Autodesk also documents AutoCAD .bak files created from DWG saves; recovery commonly involves copying the file, renaming the copy to .dwg, and opening it in AutoCAD.

Because .BAK is not a single standardized format, file type detection by extension alone is unreliable. If you do not know where the file came from, look at the folder, filename, file size, creation date, and related files nearby. A plain-text .bak may open in a text editor, while a database or CAD backup requires the original application or a compatible restore workflow.

Common MIME types: application/x-trash

Further reading

Authoritative resources for more details on the .BAK format.

Common .BAK issues

The .BAK file does not open when double-clicked

This is normal because .BAK is a generic backup extension and the operating system may not know which program created it.

  1. Look at the filename, folder, and related files to identify the original application or original extension.
  2. Try opening a copy with the program that created the backup.
  3. If the file is small and likely text-based, inspect it with a text editor.

SQL Server .BAK opens as unreadable data

A SQL Server .BAK file is a database backup, not a document or spreadsheet. It must be restored through SQL Server tools.

  1. Do not edit the .BAK file in a text editor.
  2. Use SQL Server restore functionality to restore the backup to a database.
  3. Restore to a test or non-production database first if you are unsure what the backup contains.

AutoCAD drawing backup will not open

AutoCAD .bak files are backup copies of DWG saves. They usually need to be renamed to .dwg before opening.

  1. Make a copy of the .bak file.
  2. Rename the copy so the extension is .dwg.
  3. Open the renamed copy in AutoCAD.

The restored file is corrupt or incomplete

The backup may have been interrupted, copied incompletely, created by a different application version, or not actually be the file type you expected.

  1. Compare the file size with other known-good backups from the same source.
  2. Get a fresh copy from the original system or backup location if possible.
  3. Try restoring with the exact application that created the backup, or a compatible version.

FAQ

Is every .BAK file the same format?

No. .BAK usually means backup copy. The actual format depends on the program that created it.

Can I rename a .BAK file to open it?

Sometimes. If it is clearly a backup of a known file, such as an AutoCAD .dwg backup or a text file backup, make a copy first and restore the original extension on the copy. Renaming does not convert the file.

How do I open a SQL Server .BAK file?

Use SQL Server restore functionality. A SQL Server .BAK file is a database backup and is not meant to be opened directly like a normal document.

What MIME type does .BAK use?

There is no IANA-registered MIME type specifically for .bak. Some Linux desktop systems using shared-mime-info map *.bak to application/x-trash as a generic backup file classification.

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