See the article "Formatting applied to one paragraph affects the entire document” at:
http://www.word.mvps.org/FAQs/Formatting/WholeDocumentReformatted.htm
~ Doug Robbins
Solution:
- Press Alt+F11 to display the Visual Basic Editor. Press Ctrl+G to show the Immediate Window.
Type:
ActiveDocument.Styles(wdStyleNormal).AutomaticallyUpdate = False
Press Enter, and save the document.
Note:
Styles other than Normal will let you change the "Automatically update" setting in the user interface.
Instead of using the Visual Basic Editor, you can make use of the Apply Styles pane (Ctrl+Shift+S), type in the style name, and then click Modify; in the Modify Style dialog box, clear "Automatically update" and click OK.
~ Stefan Blom
Source.