How to highlight a text by using Essential PDF?

            //Creates a new Pdfdocument.
            PdfDocument doc = new PdfDocument();
            //Adds a new Page.
            PdfPage page = doc.Pages.Add();
            //Creates a solid brush.
            PdfBrush brush = new PdfSolidBrush(System.Drawing.Color.Black);
            //Sets the font.
            PdfFont font = new PdfStandardFont(PdfFontFamily.Helvetica, 20);
            //Draws the text.
            page.Graphics.DrawString("This is Highlighted text", font, brush, new PointF(100, 50));
            //Creates a PDF text Markup annotation.
            PdfTextMarkupAnnotation textannot = new PdfTextMarkupAnnotation("Highlighted             Text", "Highlight", "This is Highlighted text", new PointF(140, 90), font);
            //Sets the Markup type as Highlight.
            textannot.TextMarkupAnnotationType = PdfTextMarkupAnnotationType.Highlight;
            //Sets the HighLight color.
            textannot.TextMarkupColor = new PdfColor(Color.Yellow);
            //Loads the annotation to page.
            page.Annotations.Add(textannot);
            //Saves the document.
            doc.Save("highlight.pdf");
            //Closes the document.
            doc.Close(true);