Without becoming paranoid, always view attachments to emails with the utmost suspicion. It's the most common way viruses are disseminated.

Having said that, a lot of important commercial communication uses attachments.

Example: The accounting program MYOB sends tax invoices as PDF files attached to an email.

"So, what's a PDF file?" You ask, wiping a fevered brow...

It means Portable Document Format and there are only 3 people in the world who know that: Me, you and the bloke who told me. The next time you meet a nerd, ask him what PDF means. He won't know, tell him and then tell him to sod off. Out of the corner of your eye, you'll see him staring at you from across the room for the rest of the evening. He is thinking you are a God.

PDF is a format created by Adobe software that creates images of documents which can then be posted on the WWW. You need a special program, Adobe Acrobat Reader, to view these files. The program can be downloaded for free. PDF files are usually very large and take a long time to load and print. To get the free Adobe Acrobat Reader download, click on this:

Now that you have the reader on your system, PDF files should automatically open.

Sometimes, you'll try to open an attachment and FRED (that's your computer, Flaming Ridiculous Electronic Device) will say "There is no program associated with this type of file. With which program do you want to open it?"

One of those clever Technicians from, Garth Ronkko, has volunteered to answer the question. Thanks Garth...

For Windows XP

Other Windows versions handle some of this differently, but the principle is the same throughout. 

If you want a quick fix, read down to the Caution Notice, and you're fixed!

It is however, recommended that you read through the background info for a full understanding.

If a file's extension is not recognised by your Operating System, there is a good chance one of the following is to blame:

1) The program that is required to open the file is not installed on your PC (as Anthony discussed above in relation to MYOB invoices sent as PDF files).

2) The required program is installed, but somehow the file 'association' has been changed.

By the way, if it's not recognised, a file should usually have an icon like this:

The simplest way to associate a file with a program is to double click the file. A window will open asking "What do you want to do?"

You should have 2 options: #1 - Use the web service to find the appropriate program and #2  - Select the program from a list.

Option #1 works well if you have an internet connection. Simply hit OK and it'll whisk you off to a Microsoft page informing you which program is known to use those files, and providing links to pages where you can get the required software.

Option #2 is for more advanced users or if you know you have the correct program installed. When you click OK with this option selected, you'll be presented with a list of the programs that are installed on your computer. Find and select the program with which you wish to open the file and click OK. The file should open in the desired program.

Caution Notice

Incorrectly altering/removing/adding file associations will not damage your system, but it may stop files from opening correctly, or opening at all.

Background Info

A file extension usually looks something like this: .exe or .jpg

Those are two of the most common. The three letters tell the computer how to access the file.

If you double click a .jpg file, a program opens up and you see a picture.

The computer knows to open it in a picture viewer because of the .jpg extension on the file name.

If you had a Word document "MyTax.doc" and renamed it to "MyTax.jpg", next time you try to open the file, your computer will try to open it in a picture viewer. It won't succeed because it's not a picture. You see now how simply changing the three letters at the end of a file name can result in files behaving differently.

The file extension determines with which program the file should be associated.

Also note: Windows HIDES the extensions of "known" file types.

For example: MyBigLetter.doc will normally appear as MyBigLetter

This is because .doc files (document files) are normally associated with Wordpad or MSWord, so Windows then hides the extension. Why? Dunno. Ask Mr Gates.

Many users consider the way Windows hides some file extensions to be highly inconvenient, and choose to show ALL file extensions, ALL the time.

You can do this yourself by doing the following:

Go to: Control panel > Folder options > Select the "View" tab and remove the tick from the check box labeled: "Hide extensions for known file types".

Anyone who got an email with AnnaKournikova.jpg attached and found out the hard way that it was ACTUALLY called AnnaKournikova.jpg.EXE and contained a virus will have disabled hidden file extensions for sure!

Ensuring you always see all file name extensions

You've been surfing the web and downloaded something containing two files...


The second, which you know is the description of how to install this thing is called:


NFO files traditionally contain text information about the package they come with, generally explaining how to install the package - An iNFO file.

However, Microsoft has recently associated .nfo files with it's System Information application.

This creates some confusion, because now there are two different formats for the same file extension.

So, if you were to double click on a traditional .nfo file, you would get an error message saying something like "This is not a valid .nfo file" when Windows tried to open it in the wrong application.

To fix this simply right click on our hypothetical file:


The Context Menu that appears (it's not actually labeled "Context Menu" but that's what its called.)

At this point, one of two things will happen:

 a) If there is no association for this file, at the top of the Context Menu list will be an option "Open" in bold.

Click "Open"

Select the radio button (little black dot) labeled "Select the program from a list"

Skip down to *** below.

 b) If there are one or more associations (there can be more than one) you will need to look on the Context Menu for the:

"Open With" option and click on it.

*** You should be presented with a list of programs installed on your PC.

The Bonza Help Centre thanks to Garth Ronkko from for this information.