MasterAdded Event [Visio 2003 SDK Documentation]
Occurs after a new master is added to a document.
Private Sub object_MasterAdded(ByVal Master As IVMaster)
object The WithEvents object that receives the event.
If you're using Microsoft Visual Basic or Visual Basic for Applications (VBA), the syntax in this topic describes a common, efficient way to handle events.
If you want to create your own Event objects, use the Add or AddAdvise method. To create an Event object that runs an add-on, use the Add method as it applies to the EventList collection. To create an Event object that receives notification, use the AddAdvise method. To find an event code for the event you want to create, see Event codes.