If you open a document in Word 2010 that was previously opened in Word 2003, you might find that it looks different – which can be annoying! Some of the default options (line spacing and so on) were changed between Word 2003 and Word 2010. If you want your documents all to look like they did in Word 2003, then:
On the Home tab, choose Change Styles then Style Set, then Word 2003. If you want this to be the default from now on, choose Change Styles then Set as Default.
If you have Office 365, you will find that Word no longer has the Change Styles option, or a style that calls itself 2003 – instead you can use the Word 2003 Look template.