Draw scalable rectangles on document

        public RadForm1()
        {
            InitializeComponent();

            this.radPdfViewer1.LoadDocument(@"..\..\Book1.pdf");
            this.radPdfViewer1.ViewerMode = FixedDocumentViewerMode.None;
            this.radPdfViewer1.PageElementCreating += radPdfViewer1_PageElementCreating; 
        }

        List<Rectangle> rectangles = new List<Rectangle>();

        private void radPdfViewer1_PageElementCreating(object sender, RadFixedPageElementEventArgs e)
        {
            e.PageElement.ElementPainted += PageElement_ElementPainted;  
            e.PageElement.MouseMove += PageElement_MouseMove;
            e.PageElement.MouseUp += PageElement_MouseUp;
        }

        private void PageElement_MouseUp(object sender, MouseEventArgs e)
        {
            RadFixedPageElement page = (sender as RadFixedPageElement);
            Rectangle pageRect = page.ControlBoundingRectangle;
            Rectangle rectInitial = new Rectangle(downLocation, new Size(Math.Abs(location.X - downLocation.X), Math.Abs(location.Y - downLocation.Y)));
            RectangleF rect = new RectangleF(new PointF(-pageRect.X + rectInitial.Location.X, -pageRect.Y + rectInitial.Location.Y), rectInitial.Size);
            
            rectangles.Add(Rectangle.Ceiling(rect));

            location = Point.Empty;
            downLocation = Point.Empty;

            this.radPdfViewer1.Invalidate(); 
        }

        Point location = Point.Empty;
        Point downLocation = Point.Empty;
        Graphics g = null;
        
        private void PageElement_MouseMove(object sender, MouseEventArgs e)
        {
            if (Control.MouseButtons == System.Windows.Forms.MouseButtons.Left)
            {
                if (downLocation == Point.Empty)
                {
                    downLocation = e.Location;
                }
                location = e.Location;
                this.radPdfViewer1.Invalidate(); 
            }
        }
       
        private void PageElement_ElementPainted(object sender, PaintEventArgs e)
        { 
            RadFixedPageElement page = (sender as RadFixedPageElement);
            Rectangle rect = page.ControlBoundingRectangle; 
            SolidBrush semiTransBrush = new SolidBrush(Color.FromArgb(128, 255, 0, 0));

            if (location != Point.Empty && downLocation != Point.Empty)
            {
                e.Graphics.ResetTransform(); 
                Rectangle r = new Rectangle(downLocation, new Size(Math.Abs(location.X - downLocation.X),
                    Math.Abs(location.Y - downLocation.Y)));
                e.Graphics.FillRectangle(semiTransBrush, r);
            }
            
            foreach (Rectangle r in rectangles)
            {
                e.Graphics.ResetTransform();  
                e.Graphics.FillRectangle(semiTransBrush, new Rectangle(new Point(rect.X + r.Location.X, rect.Y + r.Location.Y), r.Size)); 
            }
        }