title: iTextSharp.text.pdf.security.PdfPKCS7.Verify() returns false while the pdf documnet was not modified since signed
body: <p><a href="https://i.stack.imgur.com/qcToc.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qcToc.jpg" alt="C# code" /></a><img src="https://i.stack.imgur.com/GRzrM.jpg" alt="enter image description here" />I use the Verify function to verify that a digital signed pdf document was not modified since signed. Sometimes, the Verify function returns false, which means that the document was modified, while the Acrobat Reader displays an opposite message.
  While debugging the program, I discovered 2 inner fields of PdfPKCS7 class, &quot;verified&quot; and &quot;verifyResult&quot;. Before calling Verify function, both were FALSE. After the calling, &quot;verified&quot; was TRUE while &quot;verifyResult&quot; remained FALSE.
  There are 2 questions:</p>
  <ol>
  <li>Why Verify returned false while the document was not modified?</li>
  <li>Why &quot;verified&quot; field was true while Verify returned false?</li>
  </ol>