PDF Mosaic: How to add CheckBox to PDF document

using PDFMosaic;
using System;
 
namespace CheckBoxes
{
    class CheckBoxes
    {
        static void Main()
        {
            PDFDocument document = new PDFDocument();
            PDFPage page = new PDFPage(PDFPaperFormat.A4);
 
            PDFCheckBox checkBox1 = new PDFCheckBox(10, 40, 20, 20, "checkBox1");
 
            PDFCheckBox checkBox2 = new PDFCheckBox(10, 70, 20, 20, "checkBox2");
            checkBox2.Checked = true;
 
            PDFCheckBox checkBox3 = new PDFCheckBox(10, 100, 20, 20, "checkBox3");
            checkBox3.Checked = true;
            checkBox3.ReadOnly = true;
 
            page.Annotations.Add(checkBox1);
            page.Annotations.Add(checkBox2);
            page.Annotations.Add(checkBox3);
 
            PDFFont fnt = new PDFFont(PDFStandardFont.Helvetica, 10);
            PDFBrush br = new PDFSolidBrush();
 
            page.Canvas.DrawString("Unchecked", fnt, br, 35, 45);
            page.Canvas.DrawString("Checked", fnt, br, 35, 75);
            page.Canvas.DrawString("Read-only check box", fnt, br, 35, 105);
 
            document.Pages.Add(page);
            document.Save("CheckBoxes.pdf", true);
        }
    }
}