public PresentationPage GetPage( 
   int pageIndex
)

//Must be on the QueuedTask
await QueuedTask.Run(() =>
{
  //Reference a map page
  var mpage = activePresentationView.Presentation.GetPage(4) as MapPresentationPage;

  //Set the map frame extent based on the new camera's X,Y, Scale and heading values
  Camera cam = new Camera(329997.6648, 6248553.1457, 2403605.8968, 24);
  mpage.SetCamera(cam);
});

//Must be on the QueuedTask
await QueuedTask.Run(() =>
{
  //Reference map page
  var mpage = activePresentationView.Presentation.GetPage(4) as MapPresentationPage;

  //Reference map and layer
  MapProjectItem mp = Project.Current.FindItem("Page name") as MapProjectItem;
  Map map = mp.GetMap();
  FeatureLayer lyr = map.FindLayers("GreatLakes").First() as FeatureLayer;

  //Set the map frame extent to all features in the layer
  mpage.SetCamera(lyr);
});

// create customized margin and color 
CIMMargin pMargin = new CIMMargin() { Left = 0.2, Right = 0.3, Top = 0.15, Bottom = 0.25 };
CIMRGBColor pColor = new CIMRGBColor() { R = 255, G = 255, B = 0, Alpha = 50 };

//Reference a page and its transition 
var page = activePresentationView.Presentation.GetPage(0);
CIMPresentationTransition transition = page.Transition;

// update the transition style
transition.TransitionType = PresentationTransitionType.Swipe;
transition.Duration = 2.0;
transition.SwipeDirection = SwipeDirection.Top;

//Must be on the QueuedTask
await QueuedTask.Run(() =>
{
  //Set the new margin, new background color and new transition effect
  page.SetMargin(pMargin);
  page.SetBackgroundColor(pColor);
  page.SetTransition(transition);
});