how to extract QR code from pdf file in C# and save as image

You can convert the pdf pages that contain QR codes to images:

https://www.e-iceblue.com/Tutorials/Spire.PDF/Spire.PDF-Program-Guide/Convert-PDF-Page-to-Image-with-C-code.html

A solution to this would be to leverage that you have access to the BarcodeData Bounds after barcode recognition is done. This will allow you to know where the barcodes are on the page. You can then supply the bounds into the CropCommand which would allow you to extract just the QR code. Here is some sample code which demonstrates this:
 

using (RasterCodecs codecs = new RasterCodecs())
{
   CropCommand crop = new CropCommand();
   RasterImage image = codecs.Load(@"path to input file");
   BarcodeEngine barcodeEngineInstance = new BarcodeEngine();
   BarcodeData[] dataArray = barcodeEngineInstance.Reader.ReadBarcodes(image, LeadRect.Empty, 0, null);

   for (int i = 0; i < dataArray.Length; i++)
   {
      RasterImage cloneImage = image.Clone();
      BarcodeData data = dataArray[i];
      crop.Rectangle = data.Bounds; //get bounds of found barcode
      crop.Run(cloneImage); // extract just the barcode
      codecs.Save(cloneImage, @"Output path to save into file", RasterImageFormat.Png, 0); // save to output file
   }
}

https://www.leadtools.com/help/sdk/tutorials/dotnet-console-detect-and-extract-barcodes.html
https://www.leadtools.com/help/sdk/dh/l/imageprocessing-cropcommand-ctor(leadrect).html

If you want to detect the barcode location in the PDF file automatically, then crop the barcode portion and save it as image, you might need to use a programming toolkit (leadtools) that supports barcode recognition features. Also, they have image processing functions (including Crop) that can be added to a new image and saved to any supported image format. You can find more details in this article:
http://www.codeproject.com/Articles/278301/How-to-Read-Barcodes-from-Images-using-LEADTOOLS

Hi Ajit,

I would suggest that, try to convert whole or particular page of PDF file in image. Refer below link for reference
https://code.google.com/p/lib-pdf/