oleobject      loo  
    integer          li_rc  
    string            ls_orgfilename, ls_encfilename  
    string            ls_orgpathname, ls_encpathname  
    string            ls_extension = "PDF"  
    string            ls_filter = "PDF files (*.pdf),*.pdf"  
     IF GetFileOpenName ( "Select PDF file to encrypt", ls_orgpathname, ls_orgfilename, ls_extension, ls_filter ) = 1 THEN  
        IF GetFileSaveName ( "Specify filename for encrypted file", ls_encpathname, ls_encfilename, ls_extension, ls_filter ) = 1 THEN  
            loo = create oleobject  
            li_rc = loo.ConnectToNewObject ( "ItextWrapper2.ItextWrapper2" )  
    Messagebox('test',string(li_rc))
//            loo.encrypt ( ls_orgpathname, ls_encpathname )  
//            loo.DisconnectObject()  
            destroy loo  
        END IF  
    END IF

using System;
using System.Collections.Generic;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.security;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.X509;

namespace ItextWrapper2
{
    public class ItextWrapper2
    {
        public string KEYSTORE = @"C:\Users\ydulondel\AppData\Roaming\Adobe\Acrobat\11.0\Security\narval.pfx";
        public string KEYSTORE_PUB = @"D:\test\pub\CertExchangenarval.fdf";
        // public const String KEYSTORE = @"..\..\resources\text\pdf\signature\ds-ks\cert2.pfx";
        public string PASSWORD = "password";
        // public const String Src = @"..\..\resources\text\pdf\signature\xfa.pdf";
        public string Src;
        public string Dst;

        public const string HashAlg = "SHA1";
        public const string SignAlg = "SHA-1withRSA";

        private class SignatureDTO
        {
            public byte[] Hash { get; set; }
            public PdfSignatureAppearance SignatureAppearance { get; set; }
            public PdfPKCS7 Sign { get; set; }
            public DateTime Now { get; set; }
            public Stream Stream { get; set; }
        }

        private AsymmetricKeyEntry LoadCertificateChainFromKeyStorage()
        {
            MemoryStream ks = new MemoryStream();
            using (FileStream reader = new FileStream(KEYSTORE, FileMode.Open))
            {
                byte[] buffer = new byte[reader.Length];
                reader.Read(buffer, 0, (int)reader.Length);
                ks.Write(buffer, 0, buffer.Length);
                ks.Position = 0;
            }
            Pkcs12Store store = new Pkcs12Store(ks, PASSWORD.ToCharArray());
            String alias = "";
            List<X509Certificate> chain = new List<X509Certificate>();
            // searching for private key

            foreach (string al in store.Aliases)
            {
                if (store.IsKeyEntry(al) && store.GetKey(al).Key.IsPrivate)
                {
                    alias = al;
                    break;
                }
            }

            foreach (X509CertificateEntry c in store.GetCertificateChain(alias)) // may be return too
                chain.Add(c.Certificate);

            AsymmetricKeyEntry pk = store.GetKey(alias);
            return pk;
            //return chain;
        }

        public void SignTest(String pKeyStore, String pKeyStorePub, String pPassword, String pPdf, String pSignPdf)
        {
            this.KEYSTORE = pKeyStore;
            this.KEYSTORE_PUB = pKeyStorePub;
            this.PASSWORD = pPassword;
            this.Src = pPdf;
            this.Dst = pSignPdf;
            SignatureDTO result = ServerSidePrepare();
            byte[] signedData = ClientSideSign(result.Hash);
            SaveSignedDocumentOnServer(result, signedData);
        }

        private SignatureDTO ServerSidePrepare()
        {
            // get public key chain
            X509Certificate cert = new X509CertificateParser().ReadCertificate(
                File.ReadAllBytes(KEYSTORE_PUB)); // &#1089;&#1077;&#1088;&#1074;&#1077;&#1088; &#1091; &#1085;&#1072;&#1089; &#1080; &#1090;&#1072;&#1082; &#1080;&#1084;&#1077;&#1077;&#1090; &#1087;&#1091;&#1073;&#1083;&#1080;&#1095;&#1085;&#1099;&#1081; &#1082;&#1083;&#1102;&#1095; &#1087;&#1086;&#1083;&#1100;&#1079;&#1086;&#1074;&#1072;&#1090;&#1077;&#1083;&#1103;

            PdfReader reader = new PdfReader(Src); // &#1089;&#1095;&#1080;&#1090;&#1072;&#1077;&#1084; &#1095;&#1090;&#1086; &#1092;&#1072;&#1081;&#1083; &#1087;&#1077;&#1088;&#1077;&#1076; &#1087;&#1086;&#1076;&#1087;&#1080;&#1089;&#1100;&#1102; &#1077;&#1089;&#1090;&#1100; &#1085;&#1072; &#1089;&#1077;&#1088;&#1074;&#1077;&#1088;&#1077;
                                                   // MemoryStream ms = new MemoryStream();
                                                   // var ms = File.Create(Dst);
            FileStream os = new FileStream(Dst, FileMode.Create);
            PdfStamper stamper = PdfStamper.CreateSignature(reader, os, '\0');

            PdfSignatureAppearance sap = stamper.SignatureAppearance;
            sap.Reason = "reason";
            sap.Location = "location";
            sap.Certificate = cert;

            sap.SetVisibleSignature(new Rectangle(36, 748, 144, 780), 1, "sig");

            PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);

            dic.Reason = sap.Reason;
            dic.Location = sap.Location;
            dic.Contact = sap.Contact;
            // dic.Date = new PdfDate(sap.SignDate);
            dic.Date = new PdfDate(new DateTime(2015, 7, 26, 17, 5, 25));

            sap.CryptoDictionary = dic;

            Dictionary<PdfName, int> exc = new Dictionary<PdfName, int>
            {
                { PdfName.CONTENTS, 8192 * 2 + 2 }
        // &#1085;&#1077; &#1087;&#1086;&#1076;&#1087;&#1080;&#1089;&#1099;&#1074;&#1072;&#1077;&#1084;&#1099;&#1077; &#1076;&#1072;&#1085;&#1085;&#1099;&#1077; (&#1080;&#1089;&#1082;&#1083;&#1102;&#1095;&#1077;&#1085;&#1080;&#1103;). &#1047;&#1072;&#1074;&#1080;&#1089;&#1080;&#1090; &#1086;&#1090; &#1090;&#1086;&#1075;&#1086;, &#1074;&#1085;&#1077;&#1076;&#1088;&#1077;&#1085;&#1099; &#1083;&#1080; CRL &#1080; &#1086;&#1090;&#1074;&#1077;&#1090;&#1099; OCSP &#1074; &#1076;&#1086;&#1082;&#1091;&#1084;&#1077;&#1085;&#1090;&#1077;.
        // PdfName.CONTENTS &#1079;&#1076;&#1077;&#1089;&#1100; &#1076;&#1086;&#1083;&#1078;&#1077;&#1085; &#1073;&#1099;&#1090;&#1100; &#1086;&#1073;&#1103;&#1079;&#1072;&#1090;&#1077;&#1083;&#1100;&#1085;&#1086; 
      };

            sap.PreClose(exc);

            var sgn = new PdfPKCS7(null, new[] { cert }, HashAlg, false);

            Stream data = sap.GetRangeStream();
            // byte[] hash = DigestAlgorithms.Digest(data, externalDigest.getMessageDigest("SHA256"));
            byte[] messageHash = DigestAlgorithms.Digest(data, HashAlg); // hash calculated. Sending it to client.
            var now = DateTime.Now;
            return new SignatureDTO
            {
                Hash = sgn.getAuthenticatedAttributeBytes(messageHash, now, null, null, CryptoStandard.CMS),
                Now = now,
                SignatureAppearance = sap,
                Sign = sgn,
                Stream = os
            };
        }

        private byte[] ClientSideSign(byte[] hash)
        {
            AsymmetricKeyEntry pk = LoadCertificateChainFromKeyStorage();

            // we sign the hash received from the server
            ISigner sig = SignerUtilities.GetSigner(SignAlg);
            sig.Init(true, pk.Key);
            sig.BlockUpdate(hash, 0, hash.Length);
            return sig.GenerateSignature();
        }

        private void SaveSignedDocumentOnServer(SignatureDTO result, byte[] signature)
        {
            result.Sign.SetExternalDigest(signature, null, "RSA");
            byte[] encodedSig = result.Sign.GetEncodedPKCS7(result.Hash, result.Now, null, null, null, CryptoStandard.CMS);

            byte[] paddedSig = new byte[8192];
            Array.Copy(encodedSig, 0, paddedSig, 0, encodedSig.Length);

            PdfDictionary pdfDic = new PdfDictionary();
            pdfDic.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));

            result.SignatureAppearance.Close(pdfDic); // use try/catch in real app
        }
    }
}