Verify Pdf hasn't modified after adding signature?.

Hello,

I am using PDF component for adding digital signatures to the pdf document. 

Here is how I am adding the signature

   PdfLoadedDocument document = new PdfLoadedDocument("DigitalSignaturee2.pdf");

            PdfLoadedPage page = document.Pages[0] as PdfLoadedPage;

            //Creates a signature field.

            PdfSignatureField signatureField = new PdfSignatureField(page, "SignatureField");

            signatureField.Bounds = new RectangleF(0, 0, 100, 100);

            signatureField.Signature = new PdfSignature(document, page, new PdfCertificate(@"C:\Users\Public\Documents\Syncfusion\ASP.NET MVC - EJ2\16.3.0.21\App_Data\PDF\PDF.pfx", "syncfusion"), "SignatureField");

            signatureField.Signature.Reason = "I am author of this document";

            document.Form.Fields.Add(signatureField);

            document.Save();

            //Closes the document

            document.Close(true);

I can get the document certificate as of volume 4 release. But how can I verify that document hasn't modified after the signature was added. 

Here is the code for the signature retrieval.

PdfLoadedDocument loadedDocument = new PdfLoadedDocument("DigitalSignaturee2.pdf");

            //Gets the page of the document

            PdfLoadedPage page1 = loadedDocument.Pages[0] as PdfLoadedPage;

         

            PdfLoadedSignatureField field2 = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;

         

            //Get PDF Certificate instance from signature field

            PdfCertificate certificate = field2.Signature.Certificate;

            //Get the certificate details

            string subjectName = certificate.SubjectName;

            string issuerName = certificate.IssuerName;

thanks

iosman