public Layout GetLayout()

//This example references a graphic element on a layout and sets its Transparency property (which is not available in the managed API)
//by accessing the element's CIMGraphic.

//Added references
using ArcGIS.Core.CIM;                             //CIM
using ArcGIS.Desktop.Core;                         //Project
using ArcGIS.Desktop.Layouts;                      //Layout class
using ArcGIS.Desktop.Framework.Threading.Tasks;    //QueuedTask

public class GraphicElementExample1
{
  public static Task<bool> UpdateElementTransparencyAsync(string LayoutName, string ElementName, int TransValue)
  {
    //Reference a layoutitem in a project by name
    LayoutProjectItem layoutItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals(LayoutName));
    if (layoutItem == null)
      return Task.FromResult(false);

    return QueuedTask.Run<bool>(() =>
    {
      //Reference and load the layout associated with the layout item
      Layout lyt = layoutItem.GetLayout();

      //Reference a element by name
      GraphicElement graElm = lyt.FindElement(ElementName) as GraphicElement;
      if (graElm == null)
        return false;

      //Modify the Transparency property that exists only in the CIMGraphic class.
      CIMGraphic CIMGra = graElm.GetGraphic() as CIMGraphic;
      CIMGra.Transparency = TransValue;             //e.g., TransValue = 50
      graElm.SetGraphic(CIMGra);

      return true;
    });
  }
}

//Reference the layout associated with a layout project item.

LayoutProjectItem layoutItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals("Layout Name"));
Layout layout = await QueuedTask.Run(() => layoutItem.GetLayout());  //Perform on the worker thread

//Open the layout properties dialog.

//Get the layout associated with a layout project item
LayoutProjectItem lytItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals("Layout Name"));
Layout lyt = await QueuedTask.Run(() => lytItem.GetLayout());  //Worker thread

//Open the properties dialog
lyt.ShowProperties();  //GUI thread

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

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

//Use ProjectItemsChangedEvent at 3.x
ArcGIS.Desktop.Core.Events.ProjectItemsChangedEvent.Subscribe((args) => {
  //Layout added. Layout removed would be NotifyCollectionChangedAction.Remove
  if (args.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add &&
      args.ProjectItem is LayoutProjectItem layoutProjectItem)
  {
    var layout_name = layoutProjectItem.Name; 
    var layout = layoutProjectItem.GetLayout();
    System.Diagnostics.Debug.WriteLine($"Layout Added: {layout_name}");
  }
});

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

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

//Use ProjectItemsChangedEvent at 3.x
ArcGIS.Desktop.Core.Events.ProjectItemsChangedEvent.Subscribe((args) => {
  //Layout added. Layout removed would be NotifyCollectionChangedAction.Remove
  if (args.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove &&
      args.ProjectItem is LayoutProjectItem layoutProjectItem)
  {
    var layout_name = layoutProjectItem.Name;
    System.Diagnostics.Debug.WriteLine($"Layout Removed: {layout_name}");
  }
});

//Report the event args when a layout is about to be removed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.LayoutRemovingEvent.Subscribe((args) =>
//{
//  if (args.LayoutPath == "CIMPATH=layout.xml")
//  {
//    args.Cancel = true;
//  }
//  return Task.FromResult(0);
//});

//At 3.x use ProjectItemRemovingEvent
ArcGIS.Desktop.Core.Events.ProjectItemRemovingEvent.Subscribe((args) =>
{
  var layoutItems = args.ProjectItems.ToList().OfType<LayoutProjectItem>() ?? new List<LayoutProjectItem>();
  var layoutName = "DontDeleteThisOne";
  foreach(var layoutItem in layoutItems)
  {
    if (layoutItem.Name == layoutName)
    {
      args.Cancel = true;//Cancel the remove
      break;
    }
  }
  return Task.FromResult(0);
});

//Find and close all layout panes associated with a specific layout.

LayoutProjectItem findLytItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals("Layout"));
Layout findLyt = await QueuedTask.Run(() => findLytItem.GetLayout());  //Perform on the worker thread

var panes = ProApp.Panes.FindLayoutPanes(findLyt);
foreach (Pane pane in panes)
{
  ProApp.Panes.CloseLayoutPanes(findLyt.URI);  //Close the pane
}

//This sample checks to see if a layout project item already has an open application pane.  
//If it does, it checks if it is the active layout view, if not, it creates, activates and opens a new pane.

//Reference a layoutitem in a project by name
LayoutProjectItem layoutItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals("Layout View"));

//Get the layout associated with the layoutitem
Layout lyt = await QueuedTask.Run(() => layoutItem.GetLayout());
      
//Iterate through each pane in the application and check to see if the layout is already open and if so, activate it
foreach (var pane in ProApp.Panes)
{
  var layoutPane = pane as ILayoutPane;
  if (layoutPane == null)  //if not a layout pane, continue to the next pane
    continue;
  if (layoutPane.LayoutView.Layout == lyt)  //if the layout pane does match the layout, activate it.
  {
    (layoutPane as Pane).Activate();
    layoutPane.Caption = "This is a test";
    System.Windows.MessageBox.Show(layoutPane.Caption);
    return;
  }
}
//Otherwise, create, open, and activate the layout if not already open
ILayoutPane newPane = await ProApp.Panes.CreateLayoutPaneAsync(lyt);

//Zoom to the full extent of the layout
await QueuedTask.Run(() => newPane.LayoutView.ZoomTo100Percent());

//Open a layout project item in a new view.
//A layout project item may exist but it may not be open in a view. 

//Reference a layout project item by name
LayoutProjectItem someLytItem = Project.Current.GetItems<LayoutProjectItem>()
                          .FirstOrDefault(item => item.Name.Equals("MyLayout"));

//Get the layout associated with the layout project item
Layout layout = await QueuedTask.Run(() => someLytItem.GetLayout());  //Worker thread

//Create the new pane - call on UI
ILayoutPane iNewLayoutPane = await ProApp.Panes.CreateLayoutPaneAsync(layout); //GUI thread

//Change the layout page size.

//Reference the layout project item
LayoutProjectItem lytItem = Project.Current.GetItems<LayoutProjectItem>()
                         .FirstOrDefault(item => item.Name.Equals("MyLayout"));
if (layoutItem != null)
{
  await QueuedTask.Run(() =>
  {
    //Get the layout
    Layout lyt = lytItem.GetLayout();
    if (lyt != null)
    {
      //Change properties
      CIMPage page = lyt.GetPage();
      page.Width = 8.5;
      page.Height = 11;

      //Apply the changes to the layout
      lyt.SetPage(page);
    }
  });
}