What is a BAK (.bak) file?
A BAK file is a filename extension that is commonly used by many different programs to indicate one or more documents or files that are stored are backup copies, created by the program for future use.
When a program or application is saving a recently made change to a file or document and is about to overwrite the original document (such as when the user manually saves a copy of a Word document), the program will initially create a copy of the original file, with the .bak extensions added to the end of the filename. Keeping the name and simply adding the extension makes it far easier to retrieve the original document if required. Different programs and applications may use different filename extensions for the same purpose, such as “.orig” or “.old”.
Most BAK files that you would encounter on your system are created by different programs for various purposes. These can vary from an internet browser, such as Google Chrome or Firefox Mozilla, using the BAK name extension to save and backup browser bookmarks, to a system process or a program that is dedicated to saving backups from various sources.
Even though most BAK files are created by programs, a program user could also manually create one of these files. A reason for doing this could be wanting to alter a certain file or document, but also keep a copy of the original. In that case, the user would simply need to add the filename extension to the end of the file, and it will be saved as a backup file of the original.
Opening a BAK file.
Opening a BAK file can be tricky, since BAK files are fundamentally different to any other file type. Due to the fact that many different kinds of programs use this extension, there is no one application that can open every BAK file.
For example, your Music program could save a media file copy as a BAK file, the same as your Word program. You can not expect to open the BAK file Word saved with a media player and have it display the text document, or vice versa you can not expect to run a BAK media file using Word. Even though in both cases the files have the exact same filename extension, they can not both be opened by the same program, compared to for example a JPG or TXT file, where one program can open any file with that extension. The program that created the BAK file is always responsible for opening and using it.
Method 1: Reverting the file type by changing the filename extension.
So from this we can determine that no BAK file is guaranteed to be the same, and the situation where you located the BAK file in question is vitally important, as well as what kind of name the BAK file had. If the BAK file was name something like “SampleSong.bak”, a good starting off point would be to assume that it is some sort of media file and trying to open it with a media player program. You could also try renaming the file to change its format, to any media extension such as MP3 or WAV, and then attempt to open the file with the new extension.
Here is an incomplete list of programs that create and use BAK filename extensions for backup files:
- Finale Notepad
- Google Chrome
- Mozilla Firefox
- XML file
Method 2: Finding out which program created the BAK file by opening it in a text editor.
If you are still confused and can not determine which program created the file by the name or location of the BAK file, you may need to open the file with a text editor program and figure out which program created the file using the displayed text document. There are multiple great options for a free text editing programs, most notably Notepad++.
Notepad++ is really easy to start using as a beginner that just needs quick access to a text editor, but also contains advanced functionality if needed.
Here is a quick guide on how to download, install and open a file using Notepad++:
- Navigate your browser over to the Notepad++ official website at: https://notepad-plus-plus.org/ , click the “Download” button on the left, and select a version (usually the latest one) of Notepad++ you would like to download.
- You will be taken to the download page, select which download you would like. You have choice between x32 and x64 bit versions, as well as “installer” and “portable” versions. The former option will download an installer that will install the program on your system, while the latter will download a compressed pre-installed folder. Either option should be fine, so pick to your preference.
Note: You will need an extracting program such as 7-Zip or WinRAR to extract the portable installation file.
- For this example, we have chosen the installer setup. After a short download, find the installer in your download folder, and run it by double-clicking it. The installation wizard is fairly straightforward, select which install directory you would like the program installed in and click next. After the short installation Notepad++ will be installed and ready to use on your system.
- Next, navigate to the BAK file you are trying to open. Right click on it and click “Edit with Notepad++” to open the file in a text format.
- You should get a file filled with undecipherable text, similar to the one in the screenshot below.
If you look through the text, you will find certain letters and numbers that reappear throughout the file, such as “ID3” in this example. Running ID3 through google will let you know that it is a very common metadata container used for MP3 files, so it is safe to assume the BAK file was originally an MP3 file. Changing the filename extension from .bak to .mp3 will allow you to play the file on a media player.
Similarly to the MP3 file, if the BAK file was originally a CSV file you might find clues to it being originally a CSV file in the text, such as text elements or table-format elements. In this case you can do exactly the same as in the MP3 example, try changing the filename extension to the BAK file you suspect was a CSV file originally, and try opening it with Excel. If you are correct and file was originally a CSV file, it should have no issues opening.
Additionally, you could also try extracting the file using a program like WinRAR or 7-Zip. These extractors can extract a wide variety of files and could provide hints as to what the BAK file was originally.