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.
If you are currently experiencing a problem where you’re running Word or Excel and a friend sends you a document and you cannot open it then you need the compatibility pack. When Microsoft release it’s latest Office suite they changed the extension of the files from doc to docx and xls to xlsx. This means that users who run older versions of this software will not be able to open files from users who have created the file in the latest version. There is however a fix for this. Just download the Microsoft compatibility pack here.