public class SignatureLine : DocumentElement 

var signatureLineOptions = new SignatureLineOptions()
{
  AllowComments = true,
  ShowDate = true,
  Instructions = "Please sign this important document.",
  Signer = "Mark Stone",
  SignerTitle = "President",
  SignerEmail = "mark.stone@mycompany.com"
};

// Add the SignatureLine to the document.
signatureLine = document.AddSignatureLine( signatureLineOptions );

// Insert the SignatureLine in a document's paragraph.
myParagrah.AppendSignatureLine( signatureLine );