You can setup a wrapper class to enable Word's application events.
In your document, you will need to create a class module. This Class module will be called "clsEvents". Paste this code into your new class module:
Public WithEvents myApp As Word.Application
Public Sub myApp_DocumentBeforePrint(ByVal Doc As Document, Cancel As Boolean)
'add your code here
MsgBox "Blah"
End Sub
Next, create a standard module. This will be the sub that will load the application instance into your class. Name this standard module "Events". Then Paste this code:
Public e As clsEvents
Public Sub SetupEvents(theApp As Application)
Set e = New clsEvents
Set e.myApp = theApp
End Sub
Lastly, we need to call that subroutine that you just created. The easiest way to do it is to call it on the document_open event from "ThisDocument" module. Paste this code:
Private Sub Document_Open()
SetupEvents Me.Application
End Sub
This will also allow you to use all the other Word Application events that are generally hidden without the document wrapper.
Close the application, and next time the document is opened, and the user tried to print, your code will execute.
Hope that helps!