void Sign()
        {
            PdfDocument doc = new PdfDocument();
            doc.LoadFromFile(inputPath);
            //Load the certificate
            X509Certificate2 cert = new X509Certificate2(certPath, passwd);
            CustomPKCS7SignatureFormatter customPKCS7SignatureFormatter = new CustomPKCS7SignatureFormatter(cert);
            PdfSignature signature = new PdfSignature(doc, doc.Pages[0], customPKCS7SignatureFormatter, "signature0");
            signature.Bounds = new RectangleF(new PointF(90, 550), new SizeF(270, 90));
            //Set the dispay mode of graphics, if not set any, the default one will be applied
            signature.GraphicsMode = GraphicMode.SignDetail;
            signature.NameLabel = "Signer:";
            signature.Name = "gary";
            signature.ContactInfoLabel = "ContactInfo:";
            signature.DateLabel = "Date:";
            signature.Date = DateTime.Now;
            signature.LocationInfoLabel = "Location:";
            signature.LocationInfo = "Chengdu";
            signature.ReasonLabel = "Reason: ";
            signature.Reason = "The certificate of this document";
            signature.DistinguishedNameLabel = "DN: ";
            signature.DocumentPermissions = PdfCertificationFlags.AllowFormFill | PdfCertificationFlags.ForbidChanges;
            signature.SignDetailsFont = new PdfFont(PdfFontFamily.TimesRoman, 10f);
            signature.SignNameFont = new PdfFont(PdfFontFamily.Courier, 15);
            signature.SignImageLayout = SignImageLayout.None;
            //Save pdf file.
            doc.SaveToFile(outputPath, Spire.Pdf.FileFormat.PDF);
        }

        class CustomPKCS7SignatureFormatter : IPdfSignatureFormatter
        {
            /// 
            /// If encapsulate is true, a copy of the message will be included in the signature.
            /// 
            private bool m_encapsulate = true;

            /// 
            /// The signing certificate.
            /// 
            private X509Certificate2 m_certificate = null;

            public Dictionary m_parameters = new Dictionary();
            /// 
            /// Parameters for the encoding of the signature.
            /// 1.Key:Filter,String
            /// Required
            /// The name of the preferred signature handler to use when validating this signature.
            /// 2.SubFilter,String
            /// Required
            /// A name that describes the encoding of the signature value.
            /// PDF 1.6 defines the following values for public-key cryptographic signatures: adbe.x509.rsa_sha1, adbe.pkcs7.detached, and adbe.pkcs7.sha1
            /// 3.Cert,X509Certificate2
            /// Required when SubFilter is adbe.x509.rsa_sha1
            /// 
            public Dictionary Parameters
            {
                get

                { return m_parameters; }
            }

            /// 
            /// Construct a new instance.
            /// 
            /// The signing certificate.
            /// 
            /// If encapsulate is true, a copy of the message will be included in the signature.
            /// 
            public CustomPKCS7SignatureFormatter(X509Certificate2 certificate)
            {
                if (null == certificate)

                { throw new ArgumentNullException("certificate"); }
                m_certificate = certificate;
                Parameters.Add("Filter", "Adobe.PPKMS");
                Parameters.Add("SubFilter", m_encapsulate ? "adbe.pkcs7.sha1" : "adbe.pkcs7.detached");
            }

            /// 
            /// Sign.
            /// 
            /// The data that contains signature content.
            /// The signature
            public byte[] Sign(byte[] content)
            {
                CmsSigner cmsSigner = new CmsSigner(m_certificate);
                SHA1 sha1 = SHA1.Create();
                SignedCms signedCms = new SignedCms(new ContentInfo(m_encapsulate ? sha1.ComputeHash(content) : content), !m_encapsulate);
                signedCms.ComputeSignature(cmsSigner, true);
                byte[] result = signedCms.Encode();
                return result;
            }
        }

string[] files = Directory.GetFiles(@"files");
string inputFile = @"input.pdf";
string outputFile = @"output.pdf";
using (PdfDocument doc = new PdfDocument(inputFile))
{
    //Add the custom field
    doc.Collection.AddCustomField("No", "No", Spire.Pdf.Collections.CustomFieldType.NumberField);
    doc.Collection.AddFileRelatedField("FileName", "FileName", Spire.Pdf.Collections.FileRelatedFieldType.FileName);
    doc.Collection.AddFileRelatedField("Desc", "Desc", Spire.Pdf.Collections.FileRelatedFieldType.Desc);
    doc.Collection.AddFileRelatedField("CreateDate", "CreateDate", Spire.Pdf.Collections.FileRelatedFieldType.CreationDate);
    doc.Collection.AddFileRelatedField("ModDate", "ModDate", Spire.Pdf.Collections.FileRelatedFieldType.ModDate);
    doc.Collection.AddFileRelatedField("FileSize", "FileSize", Spire.Pdf.Collections.FileRelatedFieldType.Size);
    doc.Collection.AddCustomField("FileType", "FileType", Spire.Pdf.Collections.CustomFieldType.TextField);
    doc.Collection.AddCustomField("FileDate", "FileDate", Spire.Pdf.Collections.CustomFieldType.DateField);

    //Sort the file
    doc.Collection.Sort(new string[] { "No", "fileName", "Desc", "CreateDate", "ModDate", "FileSize", "FileType", "FileDate" }, new bool[] { false, true, true, true, true, true, true, true });
    for (int i = 0; i < files.Length; i++)
    {
        PdfAttachment attachment = new PdfAttachment(files[i]);
        doc.Collection.AddAttachment(attachment);
    }
    int n = 1;
    //Set the field value
    foreach (PdfAttachment att in doc.Collection.AssociatedFiles)
    {
        att.SetFieldValue("No", n);
        att.Description = n + "description";
        att.SetFieldValue("FileDate", DateTime.Today);
        att.SetFieldValue("FileType", n + "file");
        n++;
    }
    doc.SaveToFile(outputFile, FileFormat.PDF);
    doc.Dispose();
}

PdfDocument doc = new PdfDocument();
doc.LoadFromFile(inputPath);
PdfAttachment attachment = new PdfAttachment(attachmentPath);
doc.Attachments.Add(attachment,doc,Spire.Pdf.General.PdfAttachmentRelationship.Alternative);
doc.SaveToFile(outputPath);

PdfDocument pdf = new PdfDocument();
pdf.LoadFromFile(inputFile, FileFormat.PDF);
RectangleF rctg = new RectangleF(0, 0, 200, 100);
PdfTextFindCollection findCollection = pdf.Pages[0].FindText(rctg, "DEPOSIT", TextFindParameter.WholeWord);
PdfTextFindCollection findCollectionOut = pdf.Pages[0].FindText(rctg, "agreement", TextFindParameter.WholeWord);
foreach (PdfTextFind find in findCollection.Finds)
{ find.ApplyHighLight(Color.Green); }
foreach (PdfTextFind findOut in findCollectionOut.Finds)
{ findOut.ApplyHighLight(Color.Yellow); }
pdf.SaveToFile(outputFile, FileFormat.PDF);