PDF Mosaic: How to add underline annotation to PDF documents

using PDFMosaic;
using System;
 
namespace PDFUnderlineAnnotationSample
{
    class PDFUnderlineAnnotationSample
    {
        static void Main()
        {
            PDFDocument pdf = new PDFDocument();
            pdf.Pages.Add(new PDFPage(PDFPaperFormat.A4));
            PDFUnderlineAnnotation annot = new PDFUnderlineAnnotation(100, 50, 75, 50);
            annot.Contents = "PDF underline annotation";
            annot.Color = new PDFColorRGB(0, 50, 150);
 
            pdf.Pages[0].Annotations.Add(annot);
            pdf.Save("TestUnderlineAnnotation.pdf", true);
        }
    }
}