Code

public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var shapeNode = new ShapeNode()
            {
                Shape = new Shape(new ElementTemplate[]
                {
                    new LineTemplate(0, 0, 100, 0),
                    new LineTemplate(100, 0, 100, 100),
                    new LineTemplate(100, 100, 0, 100),
                }, FillRule.EvenOdd)
            };

            diagram.Nodes.Add(shapeNode);
            diagram.Nodes.First().Move(50, 50);
        }

        private void diagram_DoubleClicked(object sender, DiagramEventArgs e)
        {
            PdfExporter pdfExp = new PdfExporter();
            pdfExp.Export(diagram, @"D:\temp\diagram.pdf");
        }
    }