private void btnConvertToImages_Click(object sender, EventArgs e)
{
    if (pdfFileTextBox.Text.Trim().Equals(String.Empty))
    {
        MessageBox.Show("Please choose a source PDF file", "Choose PDF file", MessageBoxButtons.OK);
        return;
    }

    // the source pdf file
    string pdfFileName = pdfFileTextBox.Text.Trim();

    // start page number
    int startPageNumber = int.Parse(textBoxStartPage.Text.Trim());
    // end page number
    // when it is 0 the conversion will continue up to the end of document
    int endPageNumber = 0;
    if (textBoxEndPage.Text.Trim() != String.Empty)
        endPageNumber = int.Parse(textBoxEndPage.Text.Trim());

    // create the converter object and set the user options
    PdfToImageConverter pdfToImageConverter = new PdfToImageConverter();

    pdfToImageConverter.LicenseKey = "0F5PX0tPX09fSVFPX0xOUU5NUUZGRkZfTw==";

    // set the color space of the resulted images
    pdfToImageConverter.ColorSpace = SelectedColorSpace();

    // set the resolution of the resulted images
    pdfToImageConverter.Resolution = int.Parse(textBoxResolution.Text);

    // the demo output directory
    string outputDirectory = Path.Combine(Application.StartupPath, @"DemoFiles\Output");

    Cursor = Cursors.WaitCursor;

    // set the handler to be called when a page was converted
    pdfToImageConverter.PageConvertedEvent += pdfToImageConverter_PageConvertedEvent;            
            
    string outputTiffFileName = System.IO.Path.Combine(outputDirectory, "pdftoimage.tiff");
    try
    {
        if (multipageTiffCheckBox.Checked)
        {
            // save the PDF as a multipage TIFF image having a frame for each converted PDF page
            pdfToImageConverter.ConvertPdfToTiffFile(pdfFileName, startPageNumber, endPageNumber, outputTiffFileName);

            // uncomment the line below to convert PDF to a mulitpage TIFF image in memory
            //byte[] tiffImageBytes = pdfToImageConverter.ConvertPdfToTiff(pdfFileName, startPageNumber, endPageNumber);
        }
        else
        {
            // call the converter to raise the PageConvertedEvent event when a PDF page is converted
            // the pdfToImageConverter_PageConvertedEvent handler below will be executed for each converted PDF page
            pdfToImageConverter.ConvertPdfPagesToImageInEvent(pdfFileName, startPageNumber, endPageNumber);

            // Alternatively you can use the ConvertPdfPagesToImage() and ConvertPdfPagesToImageFile() methods
            // to convert the PDF pages to images in memory or to image files in a directory

            // uncomment the line below to convert PDF pages in memory to an array of PdfPageImage objects
            //PdfPageImage[] pdfPageImages = pdfToImageConverter.ConvertPdfPagesToImage(pdfFileName, startPageNumber, endPageNumber);

            // uncomment the lines below to convert PDF pages to image files in a directory
            //string outputDirectory = System.IO.Path.Combine(Application.StartupPath, @"DemoFiles\Output");
            //pdfToImageConverter.ConvertPdfPagesToImageFile(pdfFileName, startPageNumber, endPageNumber, outputDirectory, "pdfpage");
        }
    }
    catch (Exception ex)
    {
        // The conversion failed
        MessageBox.Show(String.Format("An error occurred. {0}", ex.Message), "Error");
        return;
    }
    finally
    {
        // uninstall the event handler
        pdfToImageConverter.PageConvertedEvent -= pdfToImageConverter_PageConvertedEvent;

        Cursor = Cursors.Arrow;
    }

    try
    {
        if (multipageTiffCheckBox.Checked)
        {
            System.Diagnostics.Process.Start(outputTiffFileName);
        }
        else                
        {
            System.Diagnostics.Process.Start(outputDirectory);
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(string.Format("Cannot open output folder. {0}", ex.Message));
        return;
    }
}

/// <summary>
/// The PageConvertedEvent event handler called after when a PDF page was converted to image
/// The event is raised when the ConvertPdfPagesToImageInEvent() method is used
/// </summary>
/// <param name="args">The handler argument containing the PDF page image and page number</param>
void pdfToImageConverter_PageConvertedEvent(PageConvertedEventArgs args)
{
    // get the image object and page number from even handler argument
    Image pdfPageImageObj = args.PdfPageImage.ImageObject;
    int pageNumber = args.PdfPageImage.PageNumber;

    // save the PDF page image to a PNG file
    string outputPageImage = Path.Combine(Application.StartupPath, @"DemoFiles\Output", "pdfpage_" + pageNumber + ".png");
    pdfPageImageObj.Save(outputPageImage, ImageFormat.Png);

    args.PdfPageImage.Dispose();
}