What is a BAK File?

How to Open, Edit, & Convert BAK Files

Illustration of a file being copied from one folder to another
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A file with the BAK file extension is a Backup file 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 done by anything from a web browser to store 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 your own yourself 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.

Note: Any file that has a unique extension to indicate that it's for storage, like file~, file.old, file.orig, etc., are done so for the same reason that a BAK extension may be used.

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, like 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.

For example, all of Autodesk's programs, including AutoCAD, use BAK files regularly as backup files. Other programs might as well, like your financial planning software, your tax prep program, etc. However, you can expect to open an AutoCAD .BAK file in your accounting program and expect it to somehow render your AutoCAD drawings.

No matter the software that creates it, each program is responsible for using their own BAK files when they need 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 like VLC to see if it plays. You could instead rename the file to formats you suspect the file is in, like .MP3, .WAV, etc.

User-Created BAK Files

Like I mentioned above, some BAK files are instead just renamed files that are used for safekeeping. This is usually done not only to keep a backup of the file but 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).

Note: This of course applies not only to the Windows Registry but to any file that uses an extension other than the one that the program or operating system is setup to look for and read from.

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.

Another example may be seen in an actual file on your computer, like 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 BAK format because it's not really a file format in the traditional sense, it's more of a naming scheme.

If you can't seem to figure out how to use a .BAK file I would instead recommend using Notepad++ to try reading the file's contents. There may be some text in the file that can indicate the program that created it or the type of file that it is. This can be done by right-clicking the BAK file and choosing Edit with Notepad++.

For example, a file named file.bak makes no indication whatsoever as to what type of file it is, so it's hardly an easy decision to know what program can open it. Using Notepad++ 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.

Most free zip/unzip programs can open any file type regardless of whether or not it's 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. My favorites are 7-Zip and PeaZip.

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