You need to be using templates as Paul said.
Templates in Microsoft Word
Using documents the way you are instead of templates is just asking for the problems you are experiencing.

Your users need to know to not Open the templates. If they double-click on them from within Windows, they will create a new document. Otherwise, if they use File New to access the templates that will also create a new document.

The chapter I linked to is long, but if you are running an office with multiple Word users you need every bit of information in it.