PDF Mosaic: How to add ComboBox to PDF document

using PDFMosaic;
using System;
 
namespace ComboBoxes
{
    class ComboBoxes
    {
        static void Main()
        {
            PDFDocument document = new PDFDocument();
            PDFPage page = new PDFPage(PDFPaperFormat.A4);
 
            PDFComboBox comboBox1 = new PDFComboBox(10, 40, 100, 20, "comboBox1");
            comboBox1.BorderColor = new PDFColorRGB(255, 0, 0);
            comboBox1.Font.Size = 8;
            comboBox1.Text = "Select item";
            comboBox1.Items.Add("First item");
            comboBox1.Items.Add("Second item");
            comboBox1.Items.Add("Third item");
 
            PDFComboBox comboBox2 = new PDFComboBox(10, 70, 100, 20, "comboBox2");
            comboBox2.BackgroundColor = new PDFColorRGB(0, 255, 0);
            comboBox2.Font.Size = 8;
            comboBox2.Editable = true;
            comboBox2.Text = "Editable combo box";
            comboBox2.Items.Add("First item");
            comboBox2.Items.Add("Second item");
 
            page.Annotations.Add(comboBox1);
            page.Annotations.Add(comboBox2);
 
            document.Pages.Add(page);
            document.Save("ComboBoxes.pdf", true);
        }
    }
}