Check out example codes for "itextsharp c# qr barcode examples". It will help you in understanding the concepts better.

Code Example 1

protected void Page_Load(object sender, EventArgs e)
        {
            iTextSharp.text.pdf.BarcodeQRCode qrcode = new BarcodeQRCode("testing", 50, 50, null);
            iTextSharp.text.Image img1 = qrcode.GetImage();
            Document doc = new Document();

            try
            {
                PdfWriter.GetInstance(doc, new FileStream(Server.MapPath("css") + "/Images.pdf", FileMode.Create));
                doc.Open();
                doc.Add(new Paragraph("GIF"));

                doc.Add(img1);
                MemoryStream ms = new MemoryStream(img1.OriginalData);
                System.Drawing.Image returnImage = System.Drawing.Image.FromStream(ms);

               // img = returnImage.Save(new Stream(), System.Drawing.Imaging.ImageFormat.Jpeg);

            }
            catch (Exception ex)
            {
            }
            finally
            {
                doc.Close();
            }
        }

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