File extensions in Windows are the suffixes at the end of the file name. They are usually preceded by a period as a name separator and are usually two to four characters long. It is the basic file management section, but may not be very familiar to users on foot. We will try to update you in this article.

File extensions as characters added to the name allow identify its type or format, as well as define the applications associated with each one, or what is the same, the type of software that the computer will use when running the file. There are a huge number of them to cover the wide range of formats that a personal computer can handle.

A simple example to understand its function would be handling a hypothetical file called «Windows file extensions tutorial.jpg». When we try to open this file for viewing or editing, the operating system searches for all associated applications. In this case, the .jpg extension tells us that it’s an image, so it will use the application we have installed, whether it’s internal, like Paint, or a third-party application, like Gimp or Photoshop.

As we will see later, the user you can choose to use a certain application for each file type and also have information about it without opening it just by seeing its extension.

How many extensions are there in Windows?

There are countless of them in Windows and they are distributed according to their type. Some of them are internal to the operating system, necessary for its operation, and others correspond to the large variety of formats that the computer can handle, such as image files, video files, documents, music, web and more. name some of the important ones and how it will sound:

• EXE – One of the executable file formats used to run Windows programs.
• PNG: Lossless image file format.
• DOC / DOCX – Microsoft Word text editor document file.
• HTM/HTML – Hypertext Markup Language format for creating web pages online.
• ISO – disk images for various formats
• PDF: A storage format for digital documents originally developed by Adobe.
• MP3: Compressed digital audio format.
• ZIP: compressed file format
• TXT: plain text ASCII text file.
• MPEG: compressed video file
• COM: Applications for MS-DOS

These are just a few examples of the most famous, because there are so many. Some are industry standard and others were created by the developers themselves to run specific applications.

How to view file extensions in Windows?

Microsoft doesn’t make this task easy because the latest versions of Windows don’t show extensions by default, and unless you change that, you’ll only see their name. We have already discussed this on previous occasions. In our opinion, they should be visible to users. It is not only more useful, but also safer. If file extensions are not displayed, it can be difficult to determine whether a given file (eg .jpg) is actually an image and not a malicious executable.

Its activation is simple. For example, in Windows 10, go to any Windows File Explorer window and pull down the “View” menu. A field to activate the extension will appear.

You can also activate them in View> Options> Change folder and search options> View. In the advanced configuration, you have quite a few management options, and one of them is the one we are interested in. Uncheck “Hide file extensions for known file types”.

How to select an application for each file?

Whenever you install an application in Windows that can open a certain type of file, both the file extension and the software will be included in the Windows registry. It is perfectly possible to have multiple applications that can open the same file type. You can launch the application and then load the compatible file into it. Or you can right-click the file, open its context menu, and select one of the applications that can run it. In the example, the image file is in JPG format:

However, each extension also has a default application associated with it. It’s an application that opens when you double-left-click on a file. On Windows, this is also the application that appears at the top of the list shown in the example above.

If you always use the same thing it is useful to assign an application that is always used by default with a specific file extension. To do this, right-click on the file, open its context menu and click “Choose another application”. Here you will see a list of those installed on your PC. Select the one you like and check “Always use this app to open files…” (in the example, files with the .jpg extension that will open in Photoshop 2020 by default until the user changes them.

In Windows 10, you can access the same option in System Settings > Apps > Default Apps to manage the main types of images, music, video or web files here.

Errors when changing file extensions

Windows is completely dependent on these characters to handle the execution of files, and if you remove them or change the extension, the operating system may go “crazy” and the file may be temporarily unusable. To illustrate, we renamed the .jpg image file to a .txt text file and tried to run it. The system tries to open it in Notepad and returns nonsense like the following:

To fix this, just overwrite the original extension. Windows will usually notify you of the problem with an error message before making any changes.

At this point it is worth doing a safety recommendations important and one should be very careful when opening files from untrusted sources. Especially the potentially dangerous ones in executable formats or those that run code like EXE, BAT, MSI or REG. You really have to be careful with all of them because malware can be included in any type of file.

How do you handle extensions for Linux or macOS?

Linux and macOS also use file extensions, but they don’t depend on them like Windows does. Instead, they use a protocol MIME where creators specify the file type. This information is stored in the file header, and both macOS and Linux use this information to determine what type of file they are working with.

Since file extensions aren’t really necessary on macOS or Linux, it’s quite possible that you have a valid file without an extension, but the operating system can program the file with the correct program thanks to the file information contained in its header.

Therefore, file extensions are not displayed by default on systems such as macOS. However, you can also create an Apple system display extension, and it’s probably not a bad idea for the reasons explained for Windows. The way to do this is simple, from Finder>Preferences>Advanced, enable the “Show all file name extensions” box.