What Is a BAK File?

This article describes what BAK files are, how to identify the program that created the one you're working with, and some tips about converting them.

What Is a BAK File?

A file with the BAK file extension is a backup file. This file type is used by many different applications, all for the same purpose: to store a copy of one or more files for backup purposes.

Most BAK files are created automatically by a program that needs to store a backup. This could be anything from a web browser storing backed-up bookmarks to a dedicated backup program that's archiving one or more files.

BAK files are sometimes created manually by a program's user, too. You might create one if you want to edit the file but not make changes to the original. So, instead of moving the file out of its original folder, writing over it with new data, or deleting it altogether, you might just append ".BAK" to the end of the file for safekeeping.

How to Open a BAK File

With BAK files, the context is especially important. Where did you find the BAK file? Was the BAK file named the same as another program? Answering these questions could help find the program that opens the BAK file.

It's important to realize that there is no one program that can open all BAK files, as there may be one program that can open all JPG image files or all TXT files. BAK files don't work the same way as those types of files.

There Isn't a One-Size-Fits-All App

For example, all of Autodesk's programs, including AutoCAD, use BAK files regularly as backup files. Other programs might, as well, such as your financial planning software, your tax prep program, etc. However, you can't expect to open an AutoCAD BAK file in your accounting program and have it somehow render your AutoCAD drawings.

No matter the software that creates it, each program is responsible for using its own BAK files when it needs to restore data.

If you've found a BAK file in your Music folder, for example, then it's likely that the file is some sort of media file. The quickest way to confirm this example would be to open the BAK file in a popular media player, such as VLC, to see if it plays.

You could also rename the file to a format you suspect the file is in, such as MP3, WAV, etc., and then try opening the file under that new extension.

User-Created BAK Files

As we mentioned above, some BAK files are just renamed files that are used for preserving the original file. This is usually done not only to keep a backup of the file but also to disable the file from being used.

For example, when making edits to the Windows Registry, it's usually recommended to append ".BAK" to the end of a registry key or registry value. Doing this enables you to make your own key or value with the same name in the same location but without having its name collide with the original. It also disables Windows from using the data, since it's no longer appropriately named (which is the whole reason you're making a registry edit in the first place).

Then, if a problem arises, you can just delete (or rename) your new key/file/edit, and then rename it back to the original by deleting the BAK extension. Doing this will enable Windows to properly use the key or value once again.

The Registry Could Be the Origin

Another example may be seen in an actual file on your computer, such as one that's named registrybackup.reg.bak. This type of file is really a REG file that the user didn't want to alter, so they instead made a copy of it and then named the original with a BAK extension so they could make all the changes they wanted to the copy, but never alter the original (the one with the BAK extension).

In this example, if something were to go wrong with the copy of the REG file, you could always remove the BAK extension of the original and not have to worry that it's gone forever.

This naming practice is also sometimes done with folders. Again, this is done to distinguish between the original that should be unchanged, and the one you're editing.

How to Convert a BAK File

A file converter can't convert to or from the file type BAK because it's not really a file format in the traditional sense, but more of a naming scheme. This is true no matter what format you're dealing with, for example, if you need to convert BAK to PDF, DWG, an Excel format, etc.

If you can't seem to figure out how to use a BAK file, try using a program that can open the file as a text document, such as one from our Best Free Text Editors list. There may be some text in the file that can indicate the program that created it or the type of file it is. 

Try Notepad++ for Viewing

For example, a file named file.bak makes no indication whatsoever as to what type of file it is, so it's not easy to know what program can open it. Using Notepad++ or another text editor may be helpful if you see, for example, "ID3" at the top of the file's contents. Looking this up online tells you that it's a metadata container used with MP3 files. So, renaming the file to file.mp3 may be the solution to opening that particular BAK file.

Similarly, instead of converting BAK to CSV, you might find that opening the file in a text editor shows that there's a bunch of text or table-like elements that point you to realizing that your BAK file is really a CSV file, in which case you can just rename file.bak to file.csv and open it with Excel or some other CSV editor.

Most free zip/unzip programs can open a wide range of file types, regardless of whether they're an archive file. You might try using one of them as an additional step toward figuring out what type of file the BAK file is. Our favorites are 7-Zip and PeaZip.