title: How to validate embedded signatures in PDFs on Android?
body: <p>I'm searching for a library that is able to validate embedded signatures in PDFs on Android. Does anyone know a library fulfiling the following requirements:</p>
  
  <ol>
  <li>validating whether the signed document was changed or not</li>
  <li>validating whether the certificate was manipulated</li>
  <li>validating that the certificate isn't expired</li>
  <li>resolve the certification chain to a trusted entity</li>
  </ol>
  
  <p>I have tested the following ones and they don't meet the requirements:</p>
  
  <ul>
  <li><a href="https://pdfbox.apache.org/" rel="nofollow">Apache PDFbox</a></li>
  <li><a href="http://itextpdf.com/" rel="nofollow">iTextPDF</a></li>
  <li><a href="http://pdfjet.com/" rel="nofollow">PDFjet</a></li>
  </ul>
  
  <p>I'm aware that the <a href="https://www.qoppa.com/android/pdfsdk/" rel="nofollow">Qoppa qPDF Toolkit</a> is able to solve our issues, but I don't have the required resources to obtain a license.</p>
  
  <p>Interesting side fact: I haven't even found a PDFreader app which seems to be able to show this information. If someone knows an app which provides this functionality, this information would be very much appreciated too. </p>