Using iTextSharp is possible you need to set the version of PDF and then, try this
Document doc = new Document(PageSize.A4, 50, 50, 25, 25);
PdfWriter writer = PdfWriter.GetInstance(doc, ms);
PdfContentByte contentPlacer;
writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_5);
writer.CompressionLevel = PdfStream.BEST_COMPRESSION;