Answer: Microsoft Office 2007 uses newer file formats that older versions of Microsoft Office are unable to open.
To fix this Do one or more of the following:
1. Save and distribute a copy of your document in an older file format. Saving in an older format might cause certain features in the document to be lost, so if you're not certain about what features shall be lost, keep your original and save a copy. Example:
a. Open your document, e.g., Meeting Agenda.docx.
b. Select File > Save As…. -- the Save As dialog appears.
c. Specify a new filename such as Meeting Agenda - COPY
d. In the Save as type picklist, select an older file format. In this example, select Word 97-2003 Document (*.doc).
e. Select Save.
2. If your document recipient uses Windows, ask him or her to install the following software which enables him or her to open the document:
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats
http://preview.tinyurl.com/y5a879
(microsoft.com)
This software needs to be installed only once. Afterwards, all documents created in Office 2007 will open successfully in the older version of Office.
3. If your document recipient uses OS X (Mac), ask him or her to install the following software which enables him or her to convert the document to a format compatible with Office 2004 and Office v.X. After the document has been converted, the newly converted document can be opened.
Microsoft Office Open XML File Format Converter for Mac
http://preview.tinyurl.com/2s8c6e
(microsoft.com)
This software needs to be installed only once. Afterwards, all documents converted by the converter will open successfully in the older version of Office.