Windows File Associations
Changing extensions

As discussed on the previous page, Windows associates data files with programs based on the file's extension. Thus a text file is generally associate with a text editor. In our example thus far, our file questions.txt is associated with Notepad.exe. If we were to change the association for .TXT to something else, Paint for example, text files on the system could no longer opened without first opening the ‘real’ .TXT handler and browsing for the file. Instead, Windows would return an error similar to the following:

This is because Paint is a graphics program that handles basic graphic file types such as .BMP. If we were to reverse the process and assign .BMP files to be associated with Notepad, the text editor Notepad would return a similar error.

A file that carries no extension is orphaned. In other words, it cannot be opened because no associated program has been assigned to handle it. To further explain this, let’s take the same file, questions.txt, depicted on the left of this paragraph, and change the filename so that it simply reads ‘questions’ without any extension.

When we remove the extension, Windows alerts us to this problem by prompting with the following warning:

If we proceed and say Yes, not only will the icon change (see the example to the left of this paragraph), but it will no longer be considered a .TXT file (i.e. it will no longer be automatically associated with Notepad.

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