I am first responding not to your question, but to your use of the term "master document." The Master Documents "Feature" is very problematic and would pop up in a Google or Word help search using that term. It would cause you problems.

Look into AutoText and the AutoTextList field. This is a part of Building Blocks.
Automated Boilerplate Using Microsoft Word

Otherwise what you want would require macros and programming. A UserForm comes to mind. Create & Employ a Userform