I'v found my mistake. I didn't initialize the event handler, that's why it was not firing.

So now it is working I have:

a class module
with 
Public WithEvents PPTEvent  As Application
Private Sub PPTEvent_PresentationBeforeSave(ByVal Pres As Presentation, Cancel As Boolean)

...MY code.

end sub
a standard module

Dim oEH As New classSAVE

Sub InitialiseApp()
  Set oEH.PPTEvent = Application
End Sub

I used this method (http://www.pptalchemy.co.uk/PowerPoi...Open_Code.html) to auto fire the initialiseApp part of PPT macro.