How to add bookmark on pdf file using itextsharp

 Document document = new Document(PageSize.A4, 50, 50, 25, 25);

            // Create a new PdfWriter object, specifying the output stream
         
            PdfWriter.GetInstance(document, new FileStream(Server.MapPath(“MyFirstPDF.pdf”), FileMode.Create));

            Chapter chapter1 = new Chapter(new Paragraph(“This is Chapter 1″), 1);
            Section section1 = chapter1.AddSection(20f, “Section 1.1″, 2);
            Section section2 = chapter1.AddSection(20f, “Section 1.2″, 2);
            Section subsection1 = section2.AddSection(20f, “Subsection 1.2.1″, 3);
            Section subsection2 = section2.AddSection(20f, “Subsection 1.2.2″, 3);
            Section subsubsection = subsection2.AddSection(20f, “Sub Subsection 1.2.2.1″, 4);
            Chapter chapter2 = new Chapter(new Paragraph(“This is Chapter 2″), 1);
            Section section3 = chapter2.AddSection(“Section 2.1″, 2);
            Section subsection3 = section3.AddSection(“Subsection 2.1.1″, 3);
            Section section4 = chapter2.AddSection(“Section 2.2″, 2);
            chapter1.BookmarkTitle = “Changed Title”;
            chapter1.BookmarkOpen = true;
            chapter2.BookmarkOpen = true;
            document.Add(chapter1);
            document.Add(chapter2);
            // Add the Paragraph object to the doc