// Define the PDF Document object as a class member to make it accessible in the headerHtml_NavigationCompletedEvent handler
// where the header height will be automatically adjusted
private Document pdfDocument;

// Indicates if a line should be drawn at the botom of the header
private bool drawHeaderLine = true;

protected void createPdfButton_Click(object sender, EventArgs e)
{
    // Create a PDF document
    pdfDocument = new Document();

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

    // Add a PDF page to PDF document
    PdfPage pdfPage = pdfDocument.AddPage();

    string headerHtmlUrl = Server.MapPath("~/DemoAppFiles/Input/HTML_Files/Header_HTML.html");
    try
    {
        // Add the header to PDF document
        if (autoResizeHeaderRadioButton.Checked)
        {
            // Create the document header with a default height
            // It will be automatically resized in headerHtml_NavigationCompletedEvent handler
            pdfDocument.AddHeaderTemplate(50);

            // Create a HTML element to be added in header
            HtmlToPdfElement headerHtml = new HtmlToPdfElement(headerHtmlUrl);

            // Install a handler where to create the document header based on HTML element height
            headerHtml.NavigationCompletedEvent += new NavigationCompletedDelegate(headerHtml_NavigationCompletedEvent);

            // Add the HTML element to header
            // When the element is rendered in header by converter, the headerHtml_NavigationCompletedEvent handler 
            // will be invoked and the header height will be automatically calculated
            pdfDocument.Header.AddElement(headerHtml);

            // Uninstall the handler
            headerHtml.NavigationCompletedEvent += new NavigationCompletedDelegate(headerHtml_NavigationCompletedEvent);
        }
        else
        {
            // Create the document header with a fixed height
            pdfDocument.AddHeaderTemplate(float.Parse(headerHeightTextBox.Text));

            // Create a HTML to PDF element to be added in header
            HtmlToPdfElement headerHtml = new HtmlToPdfElement(headerHtmlUrl);

            // Set the HTML element to fit the container height
            headerHtml.FitHeight = true;

            // Add HTML element to fit the fixed header height
            pdfDocument.Header.AddElement(headerHtml);

        }

        // Draw a line at the header bottom
        if (drawHeaderLine)
        {
            float headerWidth = pdfDocument.Header.Width;
            float headerHeight = pdfDocument.Header.Height;

            // Create a line element for the bottom of the header
            LineElement headerLine = new LineElement(0, headerHeight - 1, headerWidth, headerHeight - 1);

            // Set line color
            headerLine.ForeColor = Color.Gray;

            // Add line element to the bottom of the header
            pdfDocument.Header.AddElement(headerLine);
        }

        // Create a HTML to PDF element to add to document
        HtmlToPdfElement htmlToPdfElement = new HtmlToPdfElement(urlTextBox.Text);

        // Optionally set a delay before conversion to allow asynchonous scripts to finish
        htmlToPdfElement.ConversionDelay = 2;

        // Add the HTML to PDF element to document
        pdfPage.AddElement(htmlToPdfElement);

        // 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=Auto_Resize_Header_Footer.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
        pdfDocument.Close();
    }
}

/// <summary>
/// This handler is called after the navigation to header HTML completed. The document header is resized in this event handler
/// </summary>
/// <param name="eventParams">The event parameter containing the HTML content size in pixels and points</param>
void headerHtml_NavigationCompletedEvent(NavigationCompletedParams eventParams)
{
    // Get the header HTML width and height from event parameters
    float headerHtmlWidth = eventParams.HtmlContentWidthPt;
    float headerHtmlHeight = eventParams.HtmlContentHeightPt;

    // Get the header width
    float headerWidth = pdfDocument.Header.Width;

    // Calculate a resize factor to fit the header width
    float resizeFactor = 1;
    if (headerHtmlWidth > headerWidth)
        resizeFactor = headerWidth / headerHtmlWidth;

    // Calculate the header height to preserve the HTML aspect ratio
    float headerHeight = headerHtmlHeight * resizeFactor;

    if (!(headerHeight < pdfDocument.Pages[0].PageSize.Height - pdfDocument.Pages[0].Margins.Top -
                pdfDocument.Pages[0].Margins.Bottom))
    {
        throw new Exception("The header height cannot be bigger than PDF page height");
    }

    // Set the calculated header height
    pdfDocument.Header.Height = headerHeight;
}