char ch = '4';

        string pdfFile = @"C:Usersp.kulkarniDesktopPDF_FilesOCR.pdf";
        using (PdfReader reader = new PdfReader(pdfFile))
        {

            using (PdfStamper stamper = new PdfStamper(reader, new FileStream(@"D:KK_T.pdf", FileMode.Create),'4'))
            {
                stamper.FormFlattening = true;
                stamper.Writer.PdfVersion = '4';
                stamper.Writer.SetAtLeastPdfVersion('4');
                stamper.Writer.SetFullCompression();
                stamper.Writer.CompressionLevel = PdfStream.BEST_COMPRESSION;

                //stamper.CompressionLevel = PdfStream.BEST_COMPRESSION;
                stamper.SetFullCompression();

            }
        }