How to Open a BAK File
Open a BAK backup with the application that created it. BAK is a backup naming convention, not one universal format: an AutoCAD drawing backup and a SQL Server database backup require different recovery workflows.
Choose what you need
Identify the application behind a BAK file
Check its folder, base filename and neighboring files. A BAK beside a same-named DWG suggests an AutoCAD backup. A BAK in a SQL Server backup directory suggests a database backup. These clues should be confirmed with the owner before restoring anything.
Copy the backup to a separate location first. Avoid overwriting a working document or database merely to test whether the backup opens.
Open an AutoCAD BAK drawing
- Confirm the backup was created by AutoCAD.
- Copy it to a separate folder and show filename extensions in File Explorer.
- Rename the copy from .bak to .dwg.
- Open the copied drawing in compatible CAD software and inspect its contents.
For this confirmed variant, Autodesk describes the BAK as the previous drawing copy. That specific rename workflow must not be applied to unrelated backups.
Restore a SQL Server BAK backup
Use SQL Server Management Studio connected to a compatible SQL Server instance. Right-click Databases, choose Restore Database, select Device as the source and add the backup file. Review the destination name, file paths and restore options before executing the restore. Use a separate test destination when inspecting an unfamiliar backup.
A BAK is restored; an MDF database file is attached through a different workflow. Encrypted backups can require the original encryption material.
Other BAK files and missing original applications
For editor, accounting or other application backups, use that application’s documented recovery process. A readable text backup may be inspected in a text editor. Ask the sender which program produced the file if its origin is unclear.
Keep a known-good backup until you have verified the recovered content. The extension alone cannot tell you whether a BAK is obsolete or safe to delete.
Frequently asked questions
Can I rename any BAK to the original extension?
No. Renaming a copy is a documented recovery route for confirmed AutoCAD drawing backups, but other BAK files require their own application’s restore process.
Is BAK the same as MDF?
No. A SQL Server BAK is a backup used for restoration; an MDF is a database data file used in an attach workflow.
Sources and further reading
Opening routes checked against the references below on October 11, 2026. Device menus, software support and protection policies can change.