PdfReader reader = new PdfReader("HelloWorldNoMetadata.pdf");
PdfStamper stamper = new PdfStamper(reader,
 new FileOutputStream("HelloWorldStampedMetadata.pdf"));
HashMap info = reader.getInfo();
info.put("Author", "Bruno Lowagie");
info.put("Title", "Hello World stamped");
stamper.setMoreInfo(info);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
XmpWriter xmp = new XmpWriter(baos, info);
xmp.close();
stamper.setXmpMetadata(baos.toByteArray());
stamper.close();