Digitally signing a docx with no need to open the document with C#

问题

I tried this the code below but I failed to sign a document without opening it. Is it possible to sign a document with a certificate without opening it.

object TempFilePath = TemporaryFolder + FileTempName;
object Visible = false;
object readonlyfile = false;

try
{
    object missing = System.Reflection.Missing.Value;
    Microsoft.Office.Interop.Word.ApplicationClass wordapp = new
    Microsoft.Office.Interop.Word.ApplicationClass();
    Microsoft.Office.Interop.Word.Document wordDocument = wordapp.Documents.Open(ref
TempFilePath, ref missing,
    ref readonlyfile, ref missing, ref missing,
    ref missing, ref missing, ref missing,
    ref missing, ref missing, ref missing,
    ref Visible, ref missing, ref missing,
    ref missing, ref missing);

    //    wordDocument.Activate();

    //  object sigID = "{00000000-0000-0000-0000-000000000000}";

    //   wordDocument.ActiveWindow.Application.ActiveDocument.Signatures.AddSignatureLine(sigID);
    //   wordDocument.ActiveWindow.Application.ActiveDocument.Signatures.Commit();
    SignatureSet signatureSet = wordDocument.Signatures;
    Signature objSignature = signatureSet.Add();


    if (objSignature == null)
    {
        DocumentNotSigned(item);
        return false;
    }
    else
    {
        signatureSet.Commit();
        object saveChanges = true;
        wordDocument.Close(ref saveChanges, ref missing, ref missing);
        wordapp.Quit(ref missing, ref missing, ref missing);
        return true;
    }

来源：https://stackoverflow.com/questions/12258106/digitally-signing-a-docx-with-no-need-to-open-the-document-with-c-sharp