private void btnExtractImages_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 extraction 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 PDF images extractor object
    PdfImagesExtractor pdfImagesExtractor = new PdfImagesExtractor();

    pdfImagesExtractor.LicenseKey = "31FAUEJHUEBQRl5AUENBXkFCXklJSUlQQA==";

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

    Cursor = Cursors.WaitCursor;
            
    // set the handler to be called when an image was extracted
    pdfImagesExtractor.ImageExtractedEvent += pdfImagesExtractor_ImageExtractedEvent;
            
    try
    {
        // start images counting
        imageIndex = 0;

        // call the images extractor to raise the ImageExtractedEvent event when an images is extracted from a PDF page
        // the pdfImagesExtractor_ImageExtractedEvent handler below will be executed for each extracted image
        pdfImagesExtractor.ExtractImagesInEvent(pdfFileName, startPageNumber, endPageNumber);

        // Alternatively you can use the ExtractImages() and ExtractImagesToFile() methods
        // to extracted the images from a PDF document in memory or to image files in a directory

        // uncomment the line below to extract the images to an array of ExtractedImage objects
        //ExtractedImage[] pdfPageImages = pdfImagesExtractor.ExtractImages(pdfFileName, startPageNumber, endPageNumber);

        // uncomment the lines below to extract the images to image files in a directory
        //string outputDirectory = System.IO.Path.Combine(Application.StartupPath, @"DemoFiles\Output");
        //pdfImagesExtractor.ExtractImagesToFile(pdfFileName, startPageNumber, endPageNumber, outputDirectory, "pdfimage");
    }
    catch (Exception ex)
    {
        // The extraction failed
        MessageBox.Show(String.Format("An error occurred. {0}", ex.Message), "Error");
        return;
    }
    finally
    {
        // uninstall the event handler
        pdfImagesExtractor.ImageExtractedEvent -= pdfImagesExtractor_ImageExtractedEvent;

        Cursor = Cursors.Arrow;
    }

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

/// <summary>
/// The ImageExtractedEvent event handler called after an image was extracted from a PDF page.
/// The event is raised when the ExtractImagesInEvent() method is used
/// </summary>
/// <param name="args">The handler argument containing the extracted image and the PDF page number</param>
void pdfImagesExtractor_ImageExtractedEvent(ImageExtractedEventArgs args)
{
    // get the image object and page number from even handler argument
    Image pdfPageImageObj = args.ExtractedImage.ImageObject;
    int pageNumber = args.ExtractedImage.PageNumber;

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

    args.ExtractedImage.Dispose();
}