[iText-questions] Error validating signed pdf with external sign

[Josep Maria Heras]

Hello ,
I've to sign with an external sgnature. When i open de PDF and validate it, I 
get an error message that says something like
document has been modified since sign was applied

The structure of code is:
- calc the hash
- send it to the external service
- get the external signature
- put it to de dic

Can you tell me what is wrong? or where to find the error?

thanks in advance,
Josep Maria

The code:
       PdfReader reader = new PdfReader(IN_FILE);
            FileStream fout = new FileStream(OUT_FILE, FileMode.Create);

            PdfStamper stp = PdfStamper.CreateSignature(reader, fout, '\0');
            DateTime cal = DateTime.Now;

            PdfSignatureAppearance sap;
            sap = stp.SignatureAppearance;
            sap.SetVisibleSignature(new Rectangle(100, 100, 300, 200), 1, 
"Signar");

           // sap.Layer2Text = ("Prova de firma.\n\nDate: ");
            //sap.Layer2Text = ("");
            PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKMS, 
PdfName.ADBE_PKCS7_DETACHED);
            dic.Put(PdfName.TYPE, PdfName.SIG);
            dic.Put(PdfName.M, new PdfDate(cal));

            sap.CryptoDictionary = (dic);
           // sap.Acro6Layers = (true);
            int contentEstimated = 15000;
            Dictionary<PdfName, int> exc = new Dictionary<PdfName, int>();
            PdfName contingut = new PdfName("");
            exc.Add(PdfName.CONTENTS, (contentEstimated * 2 + 2));
            sap.PreClose(exc);

            IDigest messageDigest = DigestUtilities.GetDigest("SHA1");
            Stream data = sap.GetRangeStream();

            // calc the hash
            byte[] buf = new byte[8192];
            int n1;
            while ((n1 = data.Read(buf, 0, buf.Length)) > 0)
            {
                messageDigest.BlockUpdate(buf, 0, n1);
            }

            byte[] hash = new byte[messageDigest.GetDigestSize()];
            messageDigest.DoFinal(hash, 0);
            // write hash to sent it to the extenal sign util
            System.IO.File.WriteAllText("C:/Reg/hash_ToBase64.txt", 
Convert.ToBase64String(hash));
            String shash = Convert.ToBase64String(hash);
            // extenal sign util process hash
            executeExe(shash);
            // get PKCS#7
            String spk7 = System.IO.File.ReadAllText("C:/tmp/Envelope.txt");
            byte[] bpk7 = Convert.FromBase64String(spk7);

            // put the PKCS#7 to disc.
            PdfDictionary updates = new PdfDictionary();
            byte[] out1 = new byte[contentEstimated];
            System.Array.Copy(bpk7, 0, out1, 0, bpk7.Length);
            updates.Put(PdfName.CONTENTS, new 
PdfString(out1).SetHexWriting(true));
            sap.Close(updates);

Le informamos que los datos personales de esta comunicaci?n, est?n incorporados 
en un fichero bajo nuestra responsabilidad, para el tratamiento de datos de 
car?cter personal, con la finalidad de mantenerle informado sobre los servicios 
que ofrece Adhoc Synectic Systems, S.A.Vd., como interesado directo, tiene 
derecho de acceso, rectificaci?n, cancelaci?n y oposici?n al tratamiento de la 
informaci?n que le concierne y autoriza a que pase a formar parte del fichero, 
ante el cual puede ejercer sus derechos, y recibir informaci?n y publicidad de 
productos y servicios de Adhoc Synectic Systems, S.A.Los derechos precitados 
podr?n hacerse efectivos ante Adhoc Synectic Systems, S.A., Paseo Urrutia, 97, 
Local, 08042 - Barcelona, en el tel?fono 93.276.83.40 o enviando un correo 
electr?nico a ad...@ad-hoc.net.(Ley Org?nica 15/1999 de 13 de Diciembre de 
Protecci?n de Datos de Car?cter Personal). Este mensaje de correo electr?nico 
est? dirigido exclusivamente al destinatario o destinatarios indicados en el 
mismo. La informaci?n en ?l contenida puede ser confidencial y/o privada por lo 
que est? totalmente prohibida su difusi?n o reproducci?n. Si usted no es el 
destinatario de este mensaje, por favor devu?lvalo inmediatamente a la 
direcci?n de env?o y destr?yalo.

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