If someone running Microsoft Word, Excel, Powerpoint or any office application that is the 2007 version sends you a file they created there is a good chance that the file extension is .DOCX or .XLSX and you cannot open it. If you are currently running Office 2007 there is a quick file you can download to resolve the problem. It can be found here. It is called the Office compatibility pack. Once you install this you should be able to open their files.