ActiveWorkbook.BuiltinDocumentProperties("Last Save Time")
Sub Macro1()
Dim DateModif As String
DateModif = CStr(ActiveWorkbook.BuiltinDocumentProperties("Last Save Time"))
ActiveWorkbook.Names.Add Name:="DERMODIF", RefersTo:=DateModif, Visible:=False
Range("A1").Formula = "=DERMODIF"
End Sub