Microsoft Word 2007's default save format is .docx. Unfortunately older versions of word cannot open these files unless the following steps are taken:

1. Download the Compatibility Pack for the 2007 Office system
2. Update Office

Note: Even though you will now be able to open the file, some things such as equations will no longer be editable. For a full list of compatibly issues check their website

Saving a file as a .doc in Word 2007

To save a document as a .doc file so you do not have to install the compatibility pack to open it in older versions of word:

1. Click the "Office Button" on the top left of the screen
2. Move your mouse over "Save As"
3. Click "Word 97-2003 Document"


4. Type the desired file name followed by .doc
5. Click Save