It's possible to persist in the userland by abusing Microsof templates - documents that are used as base templates for all new documents created by Office. In this lab, I am abusing Ms Word templates.
Let's open and edit the base template called
Normal that can be found at:
Create a new AutoOpen macro and add your VBA code there:
Sub AutoOpen() MsgBox "Ohai from the template :)" End Sub
Save the template and exit. We're now ready to create a new document, save it and launch it - at this point, we should get our VBA code executed. Below GIF shows exactly that: