This is a Very good Tips for MSOffice 2007 users, Taken from chotocheeta.com
When you save a document under Microsoft Office by default MS Office 2007 applications uses a new file format to save the file, for example
Microsoft Word 2007 will use new file format .docx
Microsoft Excel 2007 will use new file format .xlsx
Microsoft PowerPoint 2007 will use new File format .pptx
Now when under any of these application you click Save As they will offer option to save as Older MS Office Compatible file formats,
or you can force word to save in that format by default instead of new format, By Visiting Word Options,
Then go to Save TAB (Located at the Left Navigation Panel, and under that Change the option Save file in this format to Word 97-2003 Document (.doc)
Thats it, it will force Word 2007 to save as .doc in default Save command !!!
Process is same under PowerPoint and Office Excel 2007…
Question may come why would you need it, the main reason is the Older Version of MS Office by default is not compatible with the new format, so if you send any file saved under new format will not going get open in older MS Office system. Without the Help of Microsoft Office Compatibility Pack but thats not under your control to make sure that recipient of your Document has installed that under his or her system…