protected 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 all images from HTML page
    htmlToPdfConverter.HtmlElementsMappingOptions.HtmlElementSelectors = new string[] { "img" };

    // Exclude the original images from rendering becuase they will be replaced by an image from local file system
    htmlToPdfConverter.HiddenHtmlElementsSelectors = new string[] { "img" };

    Document pdfDocument = null;
    try
    {
        // Convert a HTML string with images to replace to a PDF document object
        pdfDocument = htmlToPdfConverter.ConvertUrlToPdfDocumentObject(urlTextBox.Text);

        // Replace the images selected in HTML using special attributes with images from local file system
        foreach (HtmlElementMapping imageElementInfo in htmlToPdfConverter.HtmlElementsMappingOptions.HtmlElementsMappingResult)
        {
            PdfPage imagePdfPage = imageElementInfo.PdfRectangles[0].PdfPage;
            RectangleF imageRectangle = imageElementInfo.PdfRectangles[0].Rectangle;

            ImageElement newImageElement = new ImageElement(imageRectangle.X, imageRectangle.Y, imageRectangle.Width, imageRectangle.Height,
                            Server.MapPath("~/DemoAppFiles/Input/Images/box.jpg"));
            newImageElement.EnlargeEnabled = true;
            imagePdfPage.AddElement(newImageElement);
        }

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

        // Send the PDF as response to browser

        // Set response content type
        Response.AddHeader("Content-Type", "application/pdf");

        // Instruct the browser to open the PDF file as an attachment or inline
        Response.AddHeader("Content-Disposition", String.Format("attachment; filename=Replace_with_Higher_Quality_Images.pdf; size={0}", outPdfBuffer.Length.ToString()));

        // Write the PDF document buffer to HTTP response
        Response.BinaryWrite(outPdfBuffer);

        // End the HTTP response and stop the current page processing
        Response.End();
    }
    finally
    {
        // Close the PDF document
        if (pdfDocument != null)
            pdfDocument.Close();
    }
}