First thing is that although Normal.dotm is a global template, it is not a template that should be shared by multiple users. Each user should have his/her own Normal.dotm template. You can share customizations through other Global Templates.

Templates in Microsoft Word

Second recommendation would be to turn on the display of filename extensions in Windows. You are asking for confusion by hiding them. (Windows hides them by default because MS thinks they will scare people and make them think they are using DOS.)