using System;

using System.IO;

using System.Net;

using System.Linq;

using System.Security.Cryptography.Pkcs;

using System.Security.Cryptography.X509Certificates;

​

using iTextSharp.text;

using iTextSharp.text.pdf;

​

public class Program

{

    public static void Main()

    {

        var addr = "https://lisa.crt0.net/kk.pdf";

        byte[] bytes = new WebClient().DownloadData(addr);

        var reader = new PdfReader(bytes);

        var fields = reader.AcroFields;

        var signatureNames = fields.GetSignatureNames();

        var signatureName = signatureNames.First();

        var sDic = fields.GetSignatureDictionary(signatureName);

        var filter = sDic.GetAsName(PdfName.FILTER).ToString();

        var subfilter = sDic.GetAsName(PdfName.SUBFILTER).ToString();

        var contents = sDic.GetAsString(PdfName.CONTENTS);

        var p7bytes = contents.GetOriginalBytes();

        //var cms = SignedCms.Decode(p7bytes);

        //var p7 = fields.VerifySignature(signatureName);

        //var signDate = p7.SignDate;

        //var signName = p7.SignName;

        //signatureNames.Dump();

        //(new object[] { filter, subfilter }).Dump();

        //Convert.ToBase64String(p7).Dump();

    }

}