📖 What is a BAK File?
For a SQL Server .bak, a SQL BAK converter opens it and extracts the tables without a RESTORE.
A BAK file is a backup file, its name simply short for backup. It uses the .bak extension, and it holds a spare copy of something so you can return to that earlier version if the original goes wrong.
Countless programs make these copies. Rather than one fixed format, .bak is a habit that many pieces of software share, so what a given backup contains depends on the program that wrote it. It might be a document, a drawing, a set of settings or a whole database.
Very often a .bak is nothing more than a copy of the original with those three letters tacked on to the end of the name. That simple trick is why a backup can usually be brought back to life, and why the extension turns up in so many corners of a computer.
Key Characteristics
- Short for backup, a spare copy
- No fixed format, it spans many apps
- A safety net, for rolling back changes
- Often a renamed copy, of the original
Good to Know
- Made automatically, by many auto-saves
- Rename to restore, the usual route
- Databases differ, SQL backups are special
- Identify first, then pick the method
⚡ Quick Facts
| File Extension | .bak |
| Full Name | Backup File |
| Short For | Backup |
| Category | Backup copy |
| Standard Format | None, varies by program |
| Common Sources | Auto-saves, databases, editors |
| Usual Restore | Rename back to the original |
| Special Case | SQL Server database backups |
| Related Extensions | .bk, .tmp, .old, .dwg |
🏭 How They Are Made
Backups with this extension appear in a few recurring ways. Recognising which one you are looking at is the start of using it well.
Auto-Save
Editors quietly write a .bak as you work, so a crash or mistake leaves a fallback.
Before Overwriting
Saving over a file, a program first copies the old version to a .bak just in case.
Database Backup
Systems like SQL Server export a database to a .bak that a restore command reloads.
By Hand
You can make one yourself, copying a file and adding .bak to keep both versions.
🔎 How to Identify Yours
Since there is no single opener, the route in is to work out what the backup is a copy of. A couple of clues in the name usually give it away.
Read the full name
A name like report.docx.bak tells you plainly it is a backup of a Word document.
Look at the folder
The folder often names the app, a drawing project, a database export or a game save.
Recall the program
Think about what created it. A database tool and a text editor call for very different steps.
↩️ How to Restore It
For the everyday kind of backup, one that is a renamed copy of a document or drawing, restoring is quick. The steps below cover that common case. One thing to sort out first, though, is that your system shows file extensions at all.
Copy it first
Duplicate the .bak before touching it, so your safety net stays intact whatever happens next.
Change the extension
Rename the copy so it ends in the real extension, turning report.docx.bak into report.docx, and confirm if the system warns you.
Open it normally
Double-click the renamed file, and it loads in its usual program as an ordinary document.
🗄️ Database BAK Files
One important kind of .bak stands apart from the rest, the database backup. These are not renamed documents and cannot be opened by changing the extension.
Systems such as Microsoft SQL Server write a whole database to a .bak so it can be moved or rebuilt later. To bring it back you use the database tool itself, restoring through SQL Server Management Studio or a restore command, which reads the backup and recreates the database. Trying to rename one of these to peek inside gets you nowhere, since it holds structured database contents meant only for the system that made it.
👀 Opening to Peek Inside
Sometimes you just want to know what a mystery .bak actually is before deciding what to do with it. A plain text editor is handy for that.
Opening a backup in an editor such as Notepad++ shows its raw contents. If the text is readable, the file is likely a backup of a document or a settings file, and the words inside often reveal the source. If it looks like scrambled symbols, the backup is a binary one, such as a database or an image, and it needs its own program rather than an editor. This quick look is only for identifying the file, not for editing it.
🛡️ Handling Them Safely
A backup is only useful if it is still there when you need it, so a little care keeps a .bak doing its job.
It is also worth leaving auto-generated backups where the program put them. Many apps expect their .bak alongside the original, and moving or deleting one can remove the very safety net it was meant to be. If a backup is precious, copy it somewhere separate rather than relying on the single file in place.
🛠️ Common Issues
Most trouble with a .bak traces back to not knowing what it came from, or to treating a database backup like a simple renamed file.
| Unknown source | You cannot tell what made it. Check the full filename and folder, or peek in a text editor to spot the type. |
| Rename did nothing | Changing the extension failed to help. The backup is likely a database or binary kind that needs its own program. |
| Wrong extension guessed | Renamed to the wrong type, the file will not open. Match it to the real original, such as .dwg or .docx. |
| Damaged backup | A backup cut short or copied badly may fail to load. Some programs, such as AutoCAD with its recover command, can repair a damaged file, and failing that a second copy is the way back. |
🔀 Related Formats
A .bak sits among the other spare-copy and temporary files that programs leave behind.
.bk | A shorter spelling of the same idea, another backup copy some programs write. |
.tmp | A temporary file a program uses while working, sometimes left behind afterwards. |
.old | A previous version kept aside, named to show it has been superseded by a newer one. |
.dwg | An AutoCAD drawing, a common original that a .bak backs up as drawing.dwg.bak. |
.wbk | A Microsoft Word backup, a document-specific cousin of the generic .bak. |
❓ Frequently Asked Questions
It depends on what made the backup. The common kind is a renamed copy of a document or drawing, so you duplicate the .bak, remove the .bak from the copy's name to reveal the real extension like .docx or .dwg, then open it in its usual program. A database backup is different and cannot be opened by renaming. There is no single program that opens every .bak, so the first step is always to work out what the backup came from.
A BAK file is a backup file, its name short for backup. It is a spare copy of something, kept so you can return to that earlier version if the original is lost or damaged. Many different programs make .bak files, so there is no single format, and the contents depend on the source, from a document or drawing to a whole database. Very often a .bak is just the original file with .bak added to the end of its name.
For the everyday kind, restoring is a rename. Copy the .bak so the original backup stays safe, change the copy's name so it ends in the real extension instead of .bak, and open it as normal. So report.docx.bak becomes report.docx and loads in Word. A database backup does not work this way, since it must be brought back through a proper restore in the database program rather than by changing its name.
To give you a way back. When a program is about to overwrite a file, or as part of an auto-save, it often copies the current version to a .bak first, so a crash, a mistake or a corrupted save does not lose your work. Databases create .bak backups so a whole database can be moved or rebuilt later. In every case the idea is the same, a safety copy you can fall back on if something goes wrong with the original.
For many .bak files, yes, since they are simply the original with .bak added. Copy the file first, then change the copy's extension back to the real one, such as .docx or .dwg, and it opens normally. This does not work for every .bak, though. Database backups from SQL Server and similar tools hold structured data that a rename cannot open, and those need a formal restore inside the database program instead.
Whichever program the backup came from. A backed-up document opens in its editor once you restore the real extension, a drawing backup in its design program, and a database backup through its database tool. There is no universal .bak opener because the extension is shared by many unrelated programs. If you are not sure, a text editor like Notepad++ can show the raw contents and help you identify what the backup actually is.
Usually, but think before you do. A .bak is a backup, so deleting one removes a safety copy you might want later if the original goes wrong. If the original file is fine and you are sure you will not need to roll back, the backup can go. When in doubt, move it somewhere out of the way rather than deleting it outright, so the safety net is still there if you change your mind.
It is a database backup written by Microsoft SQL Server. Rather than a renamed document, it holds a whole database in a form the server can rebuild, so it can be moved to another machine or used to recover the data. You bring it back with a restore inside SQL Server Management Studio or a restore command, which reads the .bak and recreates the database. Renaming this kind of .bak does nothing useful, since only the database system can read it.
Often because it has been treated as the wrong kind. If renaming it changed nothing, the backup is probably a database or other binary sort that needs its own program rather than a simple extension swap. If you renamed it to the wrong extension, it will not open either, so match it to the real original. And if the backup itself was cut short or copied badly, it may be damaged, in which case another copy is the only way back.
Usually right next to the file they back up. A program that auto-saves a backup tends to place the .bak in the same folder as the original, with a matching name. Some tools let you choose a different location, and database systems write their .bak wherever the backup job points. So the quickest way to find a backup is to look in the folder of the file it protects, then check the app's own backup settings if it is not there.
Yes, and it is simple. Copy the file you want to protect and add .bak to the end of the copy's name, giving you a spare version you can keep untouched while you edit the original. If anything goes wrong, you rename the backup to the real extension and you are back where you started. This manual trick is the same idea programs use automatically, just done by hand for a file you care about.
Your system is probably hiding known file extensions, which is the default on Windows. To change that, open File Explorer, click the View tab and tick File name extensions, or in older versions clear the Hide extensions for known file types option in Folder Options. On a Mac, Finder has an equivalent setting in its preferences. Once extensions show, the .bak appears at the end of the name and you can rename it to the real extension.
AutoCAD saves a .bak of your last saved drawing in the same folder as the .dwg. To use it, make sure file extensions are visible, copy the .bak, then rename the copy from .bak to .dwg and open it in AutoCAD. If the renamed file still will not open because it is damaged, AutoCAD's recover command can often repair it. Saving the recovered drawing under a new name afterwards keeps your restored work separate and safe.
Possibly, if you act quickly. Check the recycle bin or trash first, since a deleted .bak often lands there. If it is not there, stop saving new files to that drive right away, because fresh data can overwrite the space the deleted backup used. A dedicated file-recovery tool can then scan the drive and may bring the .bak back. The sooner you try after deletion, the better the odds, so avoid using the drive in the meantime.
📝 Summary
A BAK file is a backup file, its name short for backup, and it works across many programs rather than following one fixed format. Applications create .bak copies as a safety net, whether through auto-save, before overwriting a file, or as a database export, so the contents depend entirely on the source. Very often a .bak is just the original file with .bak added to its name, which is why the usual way to restore one is to copy it, remove the .bak so it ends in the real extension like .docx or .dwg, and open it in its normal program. Database backups from Microsoft SQL Server are the main exception, since they hold a whole database and must be brought back through a proper restore rather than a rename. When a backup is a mystery, a text editor like Notepad++ can reveal whether it is readable text or binary and help identify the source. Throughout, the safe habit is to work on a copy and leave auto-generated backups where the program put them, so the safety net stays intact.