在pdf c＃中将图像水印添加到另一个图像上

全部，

我正在尝试使用itextsharp在pdf中添加图像水印。水印按预期显示在所有页面上，但是已经有图像的页面。我希望我的水印图像能够显示在pdf上的现有图像之上。
我使用以下代码添加图像

I am trying to add image watermark in pdf using itextsharp. Watermark is appearing on all the pages as expected but with ones that already have image. I want my watermarking image to come on top of the existing image on the pdf. I am using following code to add image

        using (Stream output = new FileStream(outputFile, FileMode.Create, FileAccess.Write, FileShare.None))
        {
            using (PdfStamper pdfStamper = new PdfStamper(pdfReader, output))
            {
                for (int pageIndex = 1; pageIndex <= pdfReader.NumberOfPages; pageIndex++)
                {
                    pdfStamper.FormFlattening = false;
                    iTextSharp.text.Rectangle pageRectangle = pdfReader.GetPageSizeWithRotation(pageIndex);
                    PdfContentByte pdfData = pdfStamper.GetUnderContent(pageIndex);
                    pdfData.SetFontAndSize(BaseFont.CreateFont(BaseFont.HELVETICA_BOLD, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), 10);
                    PdfGState graphicsState = new PdfGState();
                    graphicsState.FillOpacity = 0.4F;
                    pdfData.SetGState(graphicsState);
                    pdfData.BeginText();

                    iTextSharp.text.Image jpeg = iTextSharp.text.Image.GetInstance(wtrmrkimg, BaseColor.GREEN);
                    float width = pageRectangle.Width;
                    float height = pageRectangle.Height;
                    jpeg.ScaleToFit(width, height);
                    jpeg.SetAbsolutePosition(width / 2 - jpeg.Width / 2, height / 2 - jpeg.Height / 2);
                    jpeg.SetAbsolutePosition(50, 50);
                    jpeg.Rotation = 45;                       

                    pdfData.AddImage(jpeg);

                    pdfData.EndText();
                }
                pdfStamper.Close();
            }
            output.Close();
            output.Dispose();
        }

我附加当前代码的输出：

I am attaching output of the current code also :