public enum LayoutEventHint : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  

//Report the event args when a layout is changed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.LayoutChangedEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("LayoutChangedEvent:" +
//  Environment.NewLine +
//  "   arg Layout: " + args.Layout.Name);
//});

ArcGIS.Desktop.Layouts.Events.LayoutEvent.Subscribe((args) =>
{
  var layout = args.Layout;
  if (args.Hint == LayoutEventHint.PropertyChanged)
  {
    System.Diagnostics.Debug.WriteLine($"Layout PropertyChanged: {layout.Name}");
  }
});

//Report the event args when the map series properties have changed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.MapSeriesEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("MapSeriesEvent:" +
//  Environment.NewLine +
//  "   arg CurrentPageName: " + args.CurrentPageName.ToString() +
//  Environment.NewLine +
//  "   arg CurrentlPageNumber: " + args.CurrentPageNumber.ToString() +
//  Environment.NewLine +
//  "   arg Layout: " + args.Layout.Name +
//  Environment.NewLine +
//  "   arg Type: " + args.Type.ToString());
//});

ArcGIS.Desktop.Layouts.Events.LayoutEvent.Subscribe((args) =>
{
  var layout = args.Layout;
  if (args.Hint == LayoutEventHint.MapSeriesRefreshed ||
    args.Hint == LayoutEventHint.MapSeriesPageChanged)
  {
    var ms = layout.MapSeries;
    System.Diagnostics.Debug.WriteLine($"LayoutEvent {args.Hint.ToString()}: {layout.Name}");
  }
});

//Report the event args when a layout page properties are changed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.PageChangedEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("PageChangedEvent:" +
//  Environment.NewLine +
//  "   arg Layout: " + args.Layout.Name +
//  Environment.NewLine +
//  "   arg New CIMPage (height): " + args.NewPage.Height.ToString() +
//  Environment.NewLine +
//  "   arg Old CIMPage (height): " + args.OldPage.Height.ToString());
//});

ArcGIS.Desktop.Layouts.Events.LayoutEvent.Subscribe((args) =>
{
  var layout = args.Layout;
  if (args.Hint == LayoutEventHint.PageChanged)
  {
    var cimPage = args.OldPage;
    System.Diagnostics.Debug.WriteLine($"LayoutEvent {args.Hint.ToString()}: {layout.Name}");
  }
});