A docx (or dotx) file cannot hold macros. You want to save the macro in a separate template. While you could save it in the normal template, there is no good reason to do so. If you save it in a separate Global Template, one stored in the Startup Folder, you will have access to it from any document.

You can attach a QAT icon or keyboard shortcut to the macro if you want. These should also be stored in the global template.