You have probably sent a word document to a friend only to find they can't open the file since you have sent it with Office 2007 and they have an older version. 

1. Go to the flag in the circle and click. You will see two options on the bottom right of the menu.
2. Click on Word Options. 
3. On the left side, click on Save
4. On the right side, change the drop down box to WORD 97-2003 .doc
5. Click OK

Now whenever you save files in Word, you will save them in a format that people with older versions can open them.

The same goes for Excel and Powerpoint.