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A file extension is an important part of Windows that few people fully understand.  Many computers are set up so that you can't even see file extensions.  This leads to much confusion about how to open files.

A file name is made up of two parts.  There is the name of the file, which you always see, then the file extension, which you may not.  These are separated by a period.  Taking KCMalFix as an example, you download KCMalFix.exe from this site.  The file name is KCMalFix.  The file extension is EXE.  The file extension tells Windows how to open the file.  Each file type must have a program "associated" with it to open.  EXE is short for "executable" and is one of a handful of file types set by default to open themselves rather than to open with some program.

Often times I will have customers call telling me that they got a file in an email that they cannot open.  The reason is that they do not have a program installed which is "associated" with that file extension.  Let's look at a PDF file, for example.  A PDF file is an Adobe Acrobat file.  It is created with Adobe Acrobat.  There are other programs which can create a PDF, but what makes it is unimportant.  If you have Adobe Acrobat installed on your computer then when you open a PDF file it will open in Adobe Acrobat and you can edit that file.  But Adobe Acrobat is very expensive and most people don't have a need to create their own PDF files outside of printing to a PDF.  Since most of us don't have Adobe Acrobat installed on our computers, we have to open the file with something else.  That is where the file extension comes in.  When you try to open a file Windows will look at the file extension and go through its list of associations to see if it has a record of what program is used to open that file.  If there is no program installed specifically for opening that file type, Windows asks you what to open it with.

Sometimes people will try to browse for a program to open it with.  This is almost always a bad thing.  When you open a file with the wrong program Windows, by default, will usually set that program to always open files with that extension.  If it's not the right program then Windows will always open files with that extension with a program that doesn't understand the file and cannot open it.  So what do you do?  It's easy.  You use Google to research the file extension and you will easily and quickly determine what program is necessary to open that file in most cases.  For instance, a PDF file is opened with Adobe Reader.  Install Adobe Reader and it automatically sets Adobe Reader to be the program to open files with all the extensions it can open.  The next time you try to open the file it will open automatically without a problem.

There is a little confusion over Microsoft Office files as well.  Microsoft Office versions 2003 and before used the DOC extension for documents and the XLS extensions for Excel.  Stating with Microsoft Office 2007, however, the default file extensions were DOCX for documents and XLSX for Excel files.  This was done because the format of the files changed in such a way that they could not be properly interpreted by earlier versions of the programs, so they gave them different file extensions.  This confuses people because they know the document was created in Microsoft Word, they have Microsoft Word, but Windows still asks what program to open the file in.  This is because, for instance, the document was made with Microsoft Word 2010 and they have Microsoft Word 2003 on their computer, which is not capable of opening the DOCX format, only the older DOC format.  So what you must do is either upgrade to a newer version of Microsoft Office or get the Microsoft Word Viewer to view the newer file type.  (NOTE: The Microsoft Word Viewer is linked in the Software section of this site)