Choosing a File Format When Saving Office Documents on a Mac
If you don’t specify otherwise, Word will save your files in the default Office 2008 for Mac file format (.docx). In previous versions of Office, files were saved in the .doc format. That new .docx file format may not be your best choice of file format saving, however.
File sizes for files saved using the new .docx format are not much smaller and are occasionally even larger than the same document saved in the default Office 2004 file format. Furthermore, because many people are still using earlier versions of Office, if you use the new default XML file formats, those people won’t be able to open your files.
As a rule, if you’re going to be sharing Office 2008 documents with others, save them in the older Office 2004 document file format (.doc). You can use the Office 2008 for Mac Format pop-up menu in the Save sheet to choose the file format for the file you’re about to save.
Along the same lines, the new and old file formats for Excel and PowerPoint are .xlsx and .xls, respectively, for Excel files and .pptx and .ppt, respectively, for PowerPoint files. So, if you’re going to be sharing Excel or PowerPoint 2008 files with anyone, save them in the older file formats — .xls and .ppt — so that you know that anyone using the previous version of Office will be able to open your files.