private void convertToPdfButton_Click(object sender, EventArgs e)
{
    // Create a HTML to PDF converter object with default settings
    HtmlToPdfConverter htmlToPdfConverter = new HtmlToPdfConverter();

    // Set license key received after purchase to use the converter in licensed mode
    // Leave it not set to use the converter in demo mode
    htmlToPdfConverter.LicenseKey = "fvDh8eDx4fHg4P/h8eLg/+Dj/+jo6Og=";

    // Select the HTML elements for which to retrieve location and other information from HTML document
    htmlToPdfConverter.HtmlElementsMappingOptions.HtmlElementSelectors = new string[] { htmlElementsSelectorTextBox.Text };

    Cursor = Cursors.WaitCursor;

    // Convert HTML to PDF using the settings above
    string outPdfFile = @"DemoAppFiles\Output\HTML_to_PDF\Select_in_API_HTML_Elements_to_Retrieve.pdf";
    Document pdfDocument = null;
    try
    {
        // Convert HTML page to a PDF document object which can be further modified to highlight the selected elements
        pdfDocument = htmlToPdfConverter.ConvertUrlToPdfDocumentObject(urlTextBox.Text);

        // Highlight the selected elements in PDF with colored rectangles
        foreach (HtmlElementMapping htmlElementInfo in htmlToPdfConverter.HtmlElementsMappingOptions.HtmlElementsMappingResult)
        {
            // Get other information about HTML element
            string htmlElementTagName = htmlElementInfo.HtmlElementTagName;
            string htmlElementID = htmlElementInfo.HtmlElementId;

            // Hightlight the HTML element in PDF

            // A HTML element can span over many PDF pages and therefore the mapping of the HTML element in PDF document consists 
            // in a list of rectangles, one rectangle for each PDF page where this element was rendered
            foreach (HtmlElementPdfRectangle htmlElementLocationInPdf in htmlElementInfo.PdfRectangles)
            {
                // Get the HTML element location in PDF page
                PdfPage htmlElementPdfPage = htmlElementLocationInPdf.PdfPage;
                RectangleF htmlElementRectangleInPdfPage = htmlElementLocationInPdf.Rectangle;

                // Highlight the HTML element element with a colored rectangle in PDF
                RectangleElement highlightRectangle = new RectangleElement(htmlElementRectangleInPdfPage.X, htmlElementRectangleInPdfPage.Y,
                    htmlElementRectangleInPdfPage.Width, htmlElementRectangleInPdfPage.Height);

                if (htmlElementTagName.ToLower() == "h1")
                    highlightRectangle.ForeColor = Color.Blue;
                else if (htmlElementTagName.ToLower() == "h2")
                    highlightRectangle.ForeColor = Color.Green;
                else if (htmlElementTagName.ToLower() == "h3")
                    highlightRectangle.ForeColor = Color.Red;
                else if (htmlElementTagName.ToLower() == "h4")
                    highlightRectangle.ForeColor = Color.Yellow;
                else if (htmlElementTagName.ToLower() == "h5")
                    highlightRectangle.ForeColor = Color.Indigo;
                else if (htmlElementTagName.ToLower() == "h6")
                    highlightRectangle.ForeColor = Color.Orange;
                else
                    highlightRectangle.ForeColor = Color.Navy;

                highlightRectangle.LineStyle.LineDashStyle = LineDashStyle.Solid;

                htmlElementPdfPage.AddElement(highlightRectangle);
            }
        }

        // Save the PDF document in a memory buffer
        byte[] outPdfBuffer = pdfDocument.Save();

        // Write the memory buffer in a PDF file
        System.IO.File.WriteAllBytes(outPdfFile, outPdfBuffer);
    }
    catch (Exception ex)
    {
        // The HTML to PDF conversion failed
        MessageBox.Show(String.Format("HTML to PDF Error. {0}", ex.Message));
        return;
    }
    finally
    {
        // Close the PDF document
        if (pdfDocument != null)
            pdfDocument.Close();

        Cursor = Cursors.Arrow;
    }

    // Open the created PDF document in default PDF viewer
    try
    {
        System.Diagnostics.Process.Start(outPdfFile);
    }
    catch (Exception ex)
    {
        MessageBox.Show(String.Format("Cannot open created PDF file '{0}'. {1}", outPdfFile, ex.Message));
    }
}