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What Is a File Extension

It's important to understand what file extensions are and how they work, since it is the file extension that represents a type of file and which program it opens with. File extensions are used on almost all computers and operating systems and this has been since the very beginning of the digital age. There are thousands of different types of files, each of them being represented by a different file extension. For example, documents created in Microsoft Word use the DOC or DOCX file extension. This identifies that file as a document which, by default, will open in Microsoft Word when you double-click on it.

File associations entirely rely on the extension of that file. File extensions are typically three characters long, although they can be shorter or longer. In Windows, by default, the file extension is hidden from Windows Explorer. If you enable them to be visible, you'll see the file extension after the dot at the end of the file name. The reason that this feature is disabled by default is to prevent users from accidentally changing the file extension if they rename the file. Changing or removing the file extension will mean that the file will no longer be identified as the original type and you won't be able to open it just by double-clicking on it.

Assuming you do not change the default settings and file extensions remain hidden, you will still see them from time to time. When you download a file from the Internet and you have no program installed on your computer which can open the file, or you have a program installed which can open it yet is not associated with that file type, you'll be able to see the file extension in Windows Explorer. For example, say you download a video file in the MKV format. Not many programs support this format natively, so you may well find that the file you downloaded appears to be useless. What you need, however, is a program which can read MKV files (represented by the .MKV file extension). When you download and install a program which can open these files, it will normally sort out the file associations for you, although in some cases it may be necessary to deal with this manually. You can manage file associations by running "Default Programs" from the control panel in Windows Vista and later.


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