You change the setting (which is by document) for updating styles in the Templates and Addins dialog. The simplest way to get to that is on the
Developer Tab. Click on either the Word Add-Ins button or the Document Template button. The checkbox should be unchecked before it is opened on a new computer. I.e., unchecked by the originator of the document.
What happens when I send my document to someone else? Will Word mess up my formatting?