PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("test.pdf"));
PdfContentByte cb = writer.getDirectContent();
BaseFont bf= BaseFont.createFont("STSong-Light", "UniGB-UCS2-H",BaseFont.EMBEDDED);
cb.beginText();
cb.setFontAndSize(bf, 12);
cb.showTextAligned(PdfContentByte.ALIGN_CENTER, text + "This text is centered", 250, 700, 0);
cb.endText();

Image image = Image.getInstance(request.getSession().getServletContext().getRealPath("/")+"common/images/starpilot/signet.png"); 
image.scaleAbsolute(mmTopx(40), mmTopx(39));
image.setAbsolutePosition(400, flagHeight);
document.add(image);