Use iText 5.4.x to signing a PDF file

Here is a sample code to sign a PDF using iTextSharp library and it is using a certificate file (with private key).

X509Certificate2 cert = new X509Certificate2("C:\\mycert.p12");

Org.BouncyCastle.X509.X509CertificateParser cp = new Org.BouncyCastle.X509.X509CertificateParser();
Org.BouncyCastle.X509.X509Certificate[] chain = new Org.BouncyCastle.X509.X509Certificate[] {
cp.ReadCertificate(cert.RawData)};

IExternalSignature externalSignature = new X509Certificate2Signature(cert, "SHA-1");

PdfReader pdfReader = new PdfReader("C:\\multi-page-test.pdf");

var signedPdf = new FileStream("C:\\multi-page-test-signed.pdf", FileMode.Create);

var pdfStamper = PdfStamper.CreateSignature(pdfReader, signedPdf, '\0');
PdfSignatureAppearance signatureAppearance = pdfStamper.SignatureAppearance;

signatureAppearance.SignatureGraphic = Image.GetInstance("C:\\logo.png");
signatureAppearance.Reason = "Because i can";
signatureAppearance.Location = "Tu podpišem";
signatureAppearance.SetVisibleSignature(new Rectangle(100, 100, 250, 150), pdfReader.NumberOfPages, "Signature");
signatureAppearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.GRAPHIC_AND_DESCRIPTION;

MakeSignature.SignDetached(signatureAppearance, externalSignature, chain, null, null, null, 0, CryptoStandard.CMS);