You want an AutoNew macro in the template or Document_New.

AutoOpen - fires when the file holding the macro is opened.
AutoExec - fires when the file holding the macro is loaded as a global template or Add-In.
AutoNew - fires when a new document is created based on the template.

Note if you put an AutoNew or AutoOpen or Document_New or Document_Open procedure in a global template, including normal.dotm, it will act in all documents and templates!