Q: When I try to open a file that is sent to me via email, sometimes it tells me that there isn’t a program associated with the attachment. Why can’t I open these files?- Susan

A: The various types of data that a computer can work with ranges from documents, spreadsheets, databases, video, pictures, and music to a host of other less common data types.

In order for the computer to understand what type of data the file contains, it must rely on what is called the file extension. Everything before the period in a file is called the filename, while the (typically) three letters after the period is called the extension.

The ".doc" extension, for instance, tells the computer (and the user) that the file is a document and to use the program that has been "associated" with this file extension to open it (most commonly Microsoft Word).

When Microsoft Word was installed, part of the installation process is to notify Windows that it will be the program to call on whenever Windows encounters a .doc file.

Every program that you install tells Windows which file extensions that they are associated with, so Windows will know which program to call up whenever you click on a file.

When you receive a file via e-mail and get the "no association" message, you are generally given the option to choose an existing program to attempt to open the file.

The problem for most non-expert users is that they have no idea which program to choose because they have no idea what the file extension means.

The first thing you should do is reply to the sender and ask them what program is necessary to view the file or what program did they use to create the file.

If they reply with the name of a program that you already have installed, you would simply choose that program from the list that appears after you get the "no association" message.

Once you locate the program, be sure to put a checkmark in the box towards the bottom that says "Always use the selected program to open this kind of a file".

If you don’t have the program necessary to open the file, your best bet is to reply to the sender and ask if they can resend the file in a format that you can open or give you a link to a website to download the program that they are using.

Most file types are readily accessible by most users, so figuring out what can open the file based on the extension is your next step. One of the best resources on the Internet for solving these file extension mysteries is filext.com.

You can use their search feature to find the different programs that can open a file or just learn much more about file extensions in general

If a file association has not been established for a file type or you want to manually change it from one program to another, do the following:

Use My Computer or Windows Explorer to navigate to the folder that contains the file and then hold the shift key down while you right-click on the file. This should give you a dialog box with an option to "Open with…". When you choose "Open with…"?, a box with an alphabetical list of installed programs will appear.

If you know which program you want to assume the association of the file type, simply highlight it, click on the "Always use this program to open this type of file" box, then click on OK.

If you are not sure and want to experiment with various programs, leave the "Always use this program…" checkbox unmarked until you figure out exactly which program is the best choice.

Ken Colburn
President of Data Doctors Computer Services, Host of the award-winning Computer Corner radio show, and Author of Computer Q&A in the East Valley Tribune newspapers.

[tags]file extension, file extensions[/tags]