You are not using a template to generate a new document. You are opening an existing document, making changes, and then when you save the document you're probably having to be careful to use the Save As command so that you can save it with a new name and thereby avoid changing the original document. You are not using a template. You are using what would be called a boilerplate document.
If so, there's a cure!
Luckily, you can easily convert your fake templates--those boilerplate documents--to real templates.