How to associate a file name extension with an app
A file name can be associated with a default app in Windows Operating Systems. Windows Operating Systems use the default app to open files with the associated file extensions. Windows Operating Systems associate a file name with its default app, using file name extensions. For example, when you double–click a file with .xslx file name extension, Windows Operating System opens that file with Microsoft Excel app. Windows Operating System chooses Microsoft Excel app to open files with .xslx file extension, because .xslx file extension is associated with Microsoft Excel app.
I suggest you to visit the following links also, to learn more about the following topics.
• What are file name extensions
• What are known file extensions and how to view known file extensions
• Hide or Show known file name extensions in Windows Server
There are different ways to associate a file name extension with a default app. Following two sections explains two different ways to associate a file name extension with a default app.
Associate an app with a file extension using Windows Settings
Follow below steps to associate an app with a file extension using Windows Settings.
Step 01 – Open Windows Server 2025 Settings app by searching for settings in Windows Search box and then by clicking the search results, as shown in the below screenshot.
Step 02 – In Settings, click "Apps", as shown in the next screenshot.
Step 03 – In Settings > Apps > Default apps, scroll down the right–pane and then click Choose defaults by file type as shown in the below screenshot.
Step 04 – You can see the file extension and the associated app as shown in below screenshot. In below image, the marked file extension is .aac and the associated app is Windows Media Player. Windows Server 2025 will select the Windows Media Player app by default, whenever a file with .aac file extension need to be opened.
Step 05 – Find the file extension you are looking for inside Choose defaults by file types list. Click the "Choose a default" button to add a default app to the file extension, as shown in below screenshot.
Right–click the file and associate the file extension with an app
Follow below steps to associate a file extension with an app by right–clicking the file.
Step 01 – Locate the file you want to associate its file extension with an app by right–clicking the file, using your Windows File Explorer. Here in this example, we have a file named omnisecu.abc, which has an unknown file extension .abc. Let us assume that the file with .abc extension is a type of text file and you want to open the files having .abc extension with Windows text editor app (notepad.exe). Please refer below screenshot.
Step 02 – Right–click the file that has the file extension you want to associate with an app. In this example, the file name is "omnisecu.abc". Click "Open with", as shown in below image.
Step 03 – Select an app to open the file from the list. In this example the app required is "notepad.exe". Click "Choose an app on your PC", if the required app is not shown in the app list.
There are two buttons at the bottom of the "Select an app to open this file" dialog box. Click "Always" button, if you want to open the files always with the app you had selected. Click "Just once" button, if you want to open the file only this time with the app you had selected.
If you had clicked the "Choose an app on your PC" link, the Windows OpenFileDialog will be displayed and you can pick an app to open the file from your file system.
Written by Jajish Thomas.
Last updated on 21th July, 2024.