extract image from pdf

public string pdfgenera()
      {
          // Extract all images with width and height more than 200px
          SautinSoft.PdfFocus f = new SautinSoft.PdfFocus();

          string pdfFile = @"D:\ApplicationForm_10.pdf";
          string imageDir = Path.GetDirectoryName(pdfFile);

          List<PdfFocus.PdfImage> pdfImages = null;

          f.OpenPdf(pdfFile);

          if (f.PageCount > 0)
          {
              // Specify to extract only images which have width and height
              // more than 200px
              f.ImageExtractionOptions.MinSize = new System.Drawing.Size(200, 200);

              pdfImages = f.ExtractImages();

              // Show all extracted images.
              if (pdfImages != null && pdfImages.Count > 0)
              {

                  for (int i = 0; i < pdfImages.Count; i++)
                  {
                      string imageFile = Path.Combine(imageDir, String.Format("img{0}.png", i + 1));
                      pdfImages[i].Picture.Save(imageFile);
                      System.Diagnostics.Process.Start(imageFile);
                  }
              }
          }
          return "";
      }