iTextSharp.text.pdf.PdfSignatureAppearance.SetVisibleSignature C# (CSharp) Метод

        public void SetVisibleSignature(Rectangle pageRect, int page, String fieldName)
        {
            if (fieldName != null) {
                if (fieldName.IndexOf('.') >= 0)
                    throw new ArgumentException(MessageLocalization.GetComposedMessage("field.names.cannot.contain.a.dot"));
                AcroFields af = writer.AcroFields;
                AcroFields.Item item = af.GetFieldItem(fieldName);
                if (item != null)
                    throw new ArgumentException(MessageLocalization.GetComposedMessage("the.field.1.already.exists", fieldName));
                this.fieldName = fieldName;
            }
            if (page < 1 || page > writer.reader.NumberOfPages)
                throw new ArgumentException(MessageLocalization.GetComposedMessage("invalid.page.number.1", page));
            this.pageRect = new Rectangle(pageRect);
            this.pageRect.Normalize();
            rect = new Rectangle(this.pageRect.Width, this.pageRect.Height);
            this.page = page;
            newField = true;
        }

        /**
         * Signs a document with a PAdES-LTV Timestamp. The document is closed at the end.
         * @param sap the signature appearance
         * @param tsa the timestamp generator
         * @param signatureName the signature name or null to have a name generated
         * automatically
         * @throws Exception
         */
        public static void Timestamp(PdfSignatureAppearance sap, ITSAClient tsa, String signatureName) {
            int contentEstimated = tsa.GetTokenSizeEstimate();
            sap.SetVisibleSignature(new Rectangle(0,0,0,0), 1, signatureName);

            PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ETSI_RFC3161);
            dic.Put(PdfName.TYPE, PdfName.DOCTIMESTAMP);
            sap.CryptoDictionary = dic;

            Dictionary<PdfName,int> exc = new Dictionary<PdfName,int>();
            exc[PdfName.CONTENTS] = contentEstimated * 2 + 2;
            sap.PreClose(exc);
            Stream data = sap.RangeStream;
            IDigest messageDigest = DigestUtilities.GetDigest(tsa.GetDigestAlgorithm());
            byte[] buf = new byte[4096];
            int n;
            while ((n = data.Read(buf, 0, buf.Length)) > 0) {
                messageDigest.BlockUpdate(buf, 0, n);
            }
            byte[] tsImprint = new byte[messageDigest.GetDigestSize()];
            messageDigest.DoFinal(tsImprint, 0);
            byte[] tsToken = tsa.GetTimeStampToken(tsImprint);

            if (contentEstimated + 2 < tsToken.Length)
                throw new Exception("Not enough space");

            byte[] paddedSig = new byte[contentEstimated];
            System.Array.Copy(tsToken, 0, paddedSig, 0, tsToken.Length);

            PdfDictionary dic2 = new PdfDictionary();
            dic2.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));
            sap.Close(dic2);
        }