Windows File Associations

File associations allow the Windows operating system to "associate" specific file extensions with specific applications. This is how Windows decides which program to use to when you choose to do something with a file, like open or print it.

For example, if you are working in Microsoft Excel, and you save an Excel file, you know that the file name will be saved with an extension of .xls at the end of it.

That file extension of .xls tells Windows that the file can be opened, saved or printed (i.e., the file association is with) Microsoft Excel.

If the file has already been opened and saved with Excel, Windows XP can figure out it’s an Excel file, even if you change the file extension.

But if you receive an new Excel file from another source, say as an email attachment, and that file has another file extension, or no file extension at all, Windows may not be able to determine that the file is an Excel file. And if windows can't, the file won't open unless you change the file name to include the .xls extension. This is why it’s important to name your files with the correct file extensions.

Fixing File Association Errors in Windows XP

Windows keeps a list of file extensions and file associations within itself. You can see them by following these steps:

1. Open Windows Explorer by right clicking on the Start button and then clicking on Explore.
2. Click on the Tools menu, and then Folder Options.
3. Click on the File types tab.

If a specific file association gets changed or deleted, and you try to open a file that has that extension, you will get Windows errors that say essentially "this file has no program associated with it".

In other words, if I go into the File Extensions table in Windows Explorer and I delete the association between the (fictitious) .ttt extension and the MS Word program, the next time I try to double click on a .ttt file to open it, Windows will show me this error:

Then on the next dialog box, find the program that should be associated with the file and click on it.

Once you have chosen the appropriate file association, make sure that you check off the box that says "Always use the selected program to open this kind of file" to make it a permanent choice when you click OK.

You can also change the program that launches when you double click on a certain file. For example, if you want all of your .txt files to open in Word instead of in Notepad, change the .txt association to launch Word instead. Here’s a step by step article that includes some steps on how to do this.

Some file extensions should not be changed. If the file has an .exe, .com or .bat extension, don’t change it. These are "executable" programs and they won’t launch if you change that extension.

Fixing File Associations in Vista

1. Click on the round windows button on the bottom left hand corner of your screen.
2. Click on the Control Panel button
3. On Control Panel, click on Programs
4. Under Programs, click on Default Programs
5. Under Default Programs, click on Associate a file type or protocol with a program
6. Find the file extension you need to fix in the list presented. You may have to click in the list first and then scroll down
7. Highlight the file extension and then click the Change Program... button on the top right
8. Choose one of the programs recommended and then click OK.
9. Then click Close and use the red x to close out of any other windows you opened.

Here’s a list of some common and not so common file extensions and the programs that create them:

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