In Windows, how do I associate an application with a file type?

To ensure that a particular application (e.g., Notepad) handles a given file type (e.g., a .txt file):

Note: The File Extension Source lists most file extensions and their associated programs.

1. From the desktop or Start menu, select My Computer or Computer. This will open a folder that shows all of the drives located on your system.

   Note: The Windows XP default desktop view and Start menu are different from the Windows Classic View (e.g., in Windows 2000). Therefore, navigating to certain items can be different. In the interest of broad applicability, most Knowledge Base instructions assume you are using Classic View. For details about switching views, see In Windows XP, how do I switch to the Windows Classic View, Classic theme, or Classic Control Panel?

   Note: The Windows Vista Start menu and Control Panel are different from the Windows Classic View (e.g., in Windows 2000). Therefore, navigating to certain items can be different. In the interest of broad applicability, most Knowledge Base documents assume you are using the Classic View. For information about switching your Windows Vista default view to Classic View, see In Windows Vista, how do I switch to the Windows Classic Start menu or Classic Control Panel?

2. From the Tools menu, select Folder Options... .

   Note: In Windows Vista, if the menu bar is not visible at the top, press the Alt key to display the menu.

3. In the window that opens, click the File Types tab, and then click New.
   
   
4. Fill in the "File Extension" box with the file extension (the letters after the period in the filename) that you want to associate.
   
   
5. Click Advanced. This will open a field for "Associated File Type". You can select the type of file that this extension is associated with from the drop-down list, or allow Windows to specify it. Once this is completed, click OK. If the files with that extension already have an association, you will get an error that says something like:

   "Extension '.txt' is already associated with the File Type Text Document. Do you want to un-associate .txt with Text Document and create a new File Type for it?"

   If this happens, click No and see the section below on editing a file association.
   
   
6. Click Advanced, and then click New.
   
   
7. In the New Action dialog box, in the "Action" field, type: open
8. In the next field, type the full path to the application that should be used to open the file. If you don't know the full path, you can click Browse... to find it. After you finish, click OK.
   
   
9. If all the information is correct, click Close. You will see the newly created icon in the subwindow. Click Close again.

Any file with the extension you just specified will open in the associated application when you double-click the file.

Editing a file association

To edit a file association, follow the first three steps above to get to the Folder Options or Options window, and then:

1. Search the list under "Registered file types" for the program that is currently registered to open files with the extension you'd like to edit. This can be the most difficult step because the actual listing for the file type under "Registered file types:" may not match the error you received in step 5 above. You may have to highlight each item one by one and look at the extension listed under "File type details" to find the file type associated with the particular extension you wish to edit.
   
   
2. When you find the file type, highlight it and click Delete.
   
   
3. Return to step 5 above to continue creating a new file association.

Example of creating a file association

Here is a specific example of how you would associate all files that have the extension .txt with the Notepad application that comes with Windows:

1. Double-click My Computer.
   
   
2. From the Tools menu, select Folder Options... .
   
   
3. Click the File Types tab, and then click New.
   
   
4. In the "File Extension" field, enter: .txt
5. Click OK, then click Advanced, and then click New... .
   
   
6. In the "Action" field, type: open
7. In the "Application used to perform action:" field, type: c:\windows\notepad.exe
8. Click OK, and then click Close.

From now on, all files with the extension .txt will be opened by the Notepad application.

Comments/Questions/Corrections