C#

public abstract class BaseClass
{
    public abstract double SomeProperty { get; set; }
}

public class DerivedClass : BaseClass
{
    private double _fixedValue;

    public override double SomeProperty
    {
        // For the sake of argument the value is always 1d
        get { return _fixedValue; }
        set { _fixedValue = 1d; } 
    }
}

private const String ID_TIME_STAMP_TOKEN = "1.2.840.113549.1.9.16.2.14"; // RFC 3161 id-aa-timeStampToken

public void PodepisPdfCer(string SouborPDF, string OtiskCertifikatu)
{
    //http://www.dotnetportal.cz/blogy/15/Null-Reference-Exception/5250/Digitalni-podepisovani-PDF-souboru-v-C-cast-2

    //Get certificate
    //Open the currently logged-in user certificate store
    var store = new System.Security.Cryptography.X509Certificates.X509Store(System.Security.Cryptography.X509Certificates.StoreName.My, System.Security.Cryptography.X509Certificates.StoreLocation.CurrentUser);
    store.Open(System.Security.Cryptography.X509Certificates.OpenFlags.ReadOnly);

    string thumbprint = OtiskCertifikatu.Replace(" ", "").ToUpperInvariant();
    if (thumbprint[0] == 8206)
    {
        thumbprint = thumbprint.Substring(1);
    }

    //Select a certificate from the certificate store
    var certs = store.Certificates.Find(System.Security.Cryptography.X509Certificates.X509FindType.FindByThumbprint, thumbprint, true);
    store.Close();

    //Verify that a certificate exists
    if (certs.Count == 0)
    {
        MessageBox.Show("Nelze najít určený certifikát v Current user certificate store!", "Sign PDF", MessageBoxButtons.OK, MessageBoxIcon.Warning);
        return;
    }

    //Open Pdf document
    byte[] pdfData = File.ReadAllBytes(SouborPDF);

    //Sign the PDF document
    using (MemoryStream stream = new MemoryStream())
    {
        var reader = new PdfReader(pdfData);
        var stp = PdfStamper.CreateSignature(reader, stream, '\0');
        var sap = stp.SignatureAppearance;

        //Protect certain features of the document
        stp.SetEncryption(null,
            Guid.NewGuid().ToByteArray(), //random password
            PdfWriter.ALLOW_PRINTING | PdfWriter.ALLOW_COPY | PdfWriter.ALLOW_SCREENREADERS,
            PdfWriter.ENCRYPTION_AES_256);

        //Get certificate chain
        var cp = new Org.BouncyCastle.X509.X509CertificateParser();
        var certChain = new Org.BouncyCastle.X509.X509Certificate[] { cp.ReadCertificate(certs[0].RawData) };

        sap.SetCrypto(null, certChain, null, PdfSignatureAppearance.WINCER_SIGNED);

        //Set signature appearance
        BaseFont helvetica = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1250, BaseFont.EMBEDDED);
        iTextSharp.text.Font font = new iTextSharp.text.Font(helvetica, 12, iTextSharp.text.Font.NORMAL);
        sap.Layer2Font = font;
        //sap.SetVisibleSignature(new iTextSharp.text.Rectangle(415, 100, 585, 40), 1, null);

        var dic = new PdfSignature(PdfName.ADOBE_PPKMS, PdfName.ADBE_PKCS7_SHA1);
        //Set some stuff in the signature dictionary.
        dic.Date = new PdfDate(sap.SignDate);
        dic.Name = certs[0].Subject;    //Certificate name
        if (sap.Reason != null)
        {
            dic.Reason = sap.Reason;
        }
        if (sap.Location != null)
        {
            dic.Location = sap.Location;
        }

        //Set the crypto dictionary
        sap.CryptoDictionary = dic;

        //Set the size of the certificates and signature.
        int csize = 4096; //Size of the signature - 4K

        //Reserve some space for certs and signatures
        var reservedSpace = new Dictionary<PdfName, int>();
        reservedSpace[PdfName.CONTENTS] = csize * 2 + 2; //*2 because binary data is stored as hex strings. +2 for end of field
        sap.PreClose(reservedSpace);    //Actually reserve it

        //Build the signature
        System.Security.Cryptography.HashAlgorithm sha = new System.Security.Cryptography.SHA256CryptoServiceProvider();

        var sapStream = sap.GetRangeStream();
        int read = 0;
        byte[] buff = new byte[8192];
        while ((read = sapStream.Read(buff, 0, 8192)) > 0)
        {
            sha.TransformBlock(buff, 0, read, buff, 0);
        }
        sha.TransformFinalBlock(buff, 0, 0);

        //Place message in a ContentInfo object. This is required to build a SignedCms object.
        System.Security.Cryptography.Pkcs.ContentInfo contentInfo = new System.Security.Cryptography.Pkcs.ContentInfo(sha.Hash);

        //Instantiate SignedCms object with the ContentInfo above.
        //Has default SubjectIdentifierType IssuerAndSerialNumber.
        System.Security.Cryptography.Pkcs.SignedCms signedCms = new System.Security.Cryptography.Pkcs.SignedCms(contentInfo, false);

        //Formulate a CmsSigner object for the signer.
        System.Security.Cryptography.Pkcs.CmsSigner cmsSigner = new System.Security.Cryptography.Pkcs.CmsSigner(certs[0]);  //First cert in the chain is the signer cert

        //Do the whole certificate chain. This way intermediate certificates get sent across as well.
        cmsSigner.IncludeOption = System.Security.Cryptography.X509Certificates.X509IncludeOption.ExcludeRoot;

        //Časové razítko z TSA
        if (!String.IsNullOrEmpty(textBox_ServerCasovehoRazitka.Text.Trim()))
        {
            try
            {
                System.Security.Cryptography.AsnEncodedData timeData = new System.Security.Cryptography.Pkcs.Pkcs9AttributeObject(ID_TIME_STAMP_TOKEN,
                                                                                                                                  DejCasoveRazitko(stream.GetBuffer(), textBox_ServerCasovehoRazitka.Text)
                                                                                                                                 );
                cmsSigner.UnsignedAttributes.Add(timeData);
            }
            catch (Exception e)
            {
                MessageBox.Show("Chyba TSA!\n" + e.Message);
            }
        }

        //Sign the CMS/PKCS #7 message. The second argument is needed to ask for the pin.
        signedCms.ComputeSignature(cmsSigner, false);

        //Encode the CMS/PKCS #7 message.
        byte[] pk = signedCms.Encode();

        //Put the certs and signature into the reserved buffer
        byte[] outc = new byte[csize];
        Array.Copy(pk, 0, outc, 0, pk.Length);

        //Put the reserved buffer into the reserved space
        PdfDictionary certificateDictionary = new PdfDictionary();
        //certificateDictionary.Put(PdfName.CONTENTS, new PdfString(outc).SetHexWriting(true));

        //Write the signature
        sap.Close(certificateDictionary);

        //Close the stamper and save it
        stp.Close();

        reader.Close();

        byte[] signedData = stream.GetBuffer();
        File.WriteAllBytes(SouborPDF, signedData);
    }
}

static protected byte[] DejCasoveRazitko(byte[] PDF, string ServerTSA)
{
    System.Security.Cryptography.SHA256Managed hashString = new System.Security.Cryptography.SHA256Managed();
    string hex = "";

    var hashValue = hashString.ComputeHash(PDF);
    foreach (byte x in hashValue)
    {
        hex += String.Format("{0:x2}", x);
    }

    // VSTUPEM je hash dokumentu, pro který se razítko vyžaduje
    NotservisTSA.GetTimeStampRequest Request = new NotservisTSA.GetTimeStampRequest(new NotservisTSA.GetTimeStampRequestBody(hex, 0));

    NotservisTSA.Print2PDF_WebServiceSoap Soap = new NotservisTSA.Print2PDF_WebServiceSoapClient();

    ((NotservisTSA.Print2PDF_WebServiceSoapClient)Soap).Endpoint.Address = new System.ServiceModel.EndpointAddress(new Uri(ServerTSA + "/Default.asmx"));

    PodepsaniPDF.NotservisTSA.GetTimeStampResponse Response = Soap.GetTimeStamp(Request);

    // VÝSTUPEM je zakódované časové razítko (GetTimeStampResult - BASE-64 v kódované struktuře TimeStampResp, viz RFC 3161) a návratová hodnota s případným popisem chyby.
    byte[] responseBytes = Encoding.ASCII.GetBytes(Response.Body.GetTimeStampResult);

    if(!String.IsNullOrEmpty(Response.Body.Error))
        MessageBox.Show(Response.Body.Error, "Chyba", MessageBoxButtons.OK, MessageBoxIcon.Error);

    string base64String = Encoding.UTF8.GetString(responseBytes, 0, responseBytes.Length);
    return Convert.FromBase64String(base64String);
}

using (SqlConnection connection = new SqlConnection(GlobalStr.sqlConnStringMetadata))
                {
                    try
                    {
                        connection.Open();

                        /*
                         * DRW 3/10/2016
                         * Added the following Transaction object in order to set the isolation level of all queries
                         * run from MAnDA to to Read Uncommited.
                         */
                        SqlTransaction Transaction = connection.BeginTransaction(IsolationLevel.ReadUncommitted);

                        using (SqlCommand testQuery = new SqlCommand(GlobalStr.previewQueryString, connection))
                        {
                            /*
                             * DRW 3/11/2016
                             * User sets the query timeout value via a textbox on the main form. The value is held in a variable.
                             * testQuery.CommandTimeout = 300;
                             */

                            testQuery.CommandTimeout = m_QueryTimeout;
                            testQuery.Transaction = Transaction;                           

                            using (SqlDataAdapter adapter3 = new SqlDataAdapter(testQuery))
                            {
                                adapter3.Fill(GlobalData.g_queryData);

                                // Open the DataSetViewer form and send the table to it
                                DataSetViewer dsv = new DataSetViewer();
                                dsv.SetSource(GlobalData.g_queryData);
                                // set the dataview classification 05272015
                                string strClassification = string.Format("{0} {1}", GlobalStr.g_classification, GlobalStr.g_releaseability);
                                dsv.setClassification(strClassification);
                                Cursor.Current = Cursors.Default;
                                dsv.ShowDialog();

                                //dataGridView1.DataSource = GlobalData.g_queryData;
                            }
                        }
                        connection.Close();
                    }
                    catch (Exception ex)
                    {
                        /// Print error message
                        MessageBox.Show("The query test failed: " + ex.Message);
                        return;
                    }
                }