Java - que me falta para la firma con itext?

KeyStore keyStore = KeyStore.getInstance("JKS");

String pass = "456123789"; //PASSWORD DE LA KEYSTORE

java.io.FileInputStream file = new java.io.FileInputStream(

		"C:\\jks\\keystore.jks"); //EL ARCHIVO QUE GENERAMOS TIENE QUE ESTAR EN EL DISCO C

keyStore.load(file, pass.toCharArray());

PrivateKey pk = (PrivateKey) keyStore.getKey("mtorre4580",

		pass.toCharArray());//USUARIO Y PASSWORD DE LA KEYSTORE

Certificate[] chain = keyStore.getCertificateChain("mtorre4580"); //OBTENGO EL CERTIFICADO

PdfReader reader = new PdfReader(origen);

FileOutputStream os = new FileOutputStream(destino);

PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');

PdfSignatureAppearance appearance = stamper

		.getSignatureAppearance();

appearance.setReason("Firmar documento con itext mtorre4580");

appearance.setLocation("Argentina");

appearance.setVisibleSignature(new Rectangle(72, 732, 144, 780), 1,

		"signature");