Example:

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
builder.writeln("Contents of signed PDF.");

CertificateHolder certificateHolder = CertificateHolder.create(getMyDir() + "morzal.pfx", "aw");

// Create a "PdfSaveOptions" object that we can pass to the document's "Save" method
// to modify how that method converts the document to .PDF.
PdfSaveOptions options = new PdfSaveOptions();

// Configure the "DigitalSignatureDetails" object of the "SaveOptions" object to
// digitally sign the document as we render it with the "Save" method.
Calendar calendar = Calendar.getInstance();
calendar.set(2015, Calendar.JULY, 20);
Date signingTime = calendar.getTime();
options.setDigitalSignatureDetails(new PdfDigitalSignatureDetails(certificateHolder, "Test Signing", "My Office", signingTime));
options.getDigitalSignatureDetails().setHashAlgorithm(PdfDigitalSignatureHashAlgorithm.RIPE_MD_160);

Assert.assertEquals(options.getDigitalSignatureDetails().getReason(), "Test Signing");
Assert.assertEquals(options.getDigitalSignatureDetails().getLocation(), "My Office");
Assert.assertEquals(DocumentHelper.getLocalDate(options.getDigitalSignatureDetails().getSignatureDate()), DocumentHelper.getLocalDate(signingTime));

doc.save(getArtifactsDir() + "PdfSaveOptions.PdfDigitalSignature.pdf", options);