title: Insert digital signature into existing pdf file
body: <p>I need to insert a digital signature into already existing pdf files, using a rails application server. (Basically, clients upload pdf files and the server signs them with a local certificate)</p>
  
  <p>I've been using JSignpdf to insert digital signatures into pdf files, and started probing for gems for ruby...</p>
  
  <p>I've found another portable file to do this job on rubypdf site <a href="http://soft.rubypdf.com/software/pdf-digital-signe" rel="nofollow noreferrer">http://soft.rubypdf.com/software/pdf-digital-signe</a>, but cannot find any gem or even example code to do this in ruby.</p>
  
  <p>I've looked also at <a href="https://stackoverflow.com/questions/1999096/digital-signature-verification-with-openssl">Digital signature verification with OpenSSL</a>, but couldn't understand how to actually sign an already existing document, with a local certificate file.</p>
  
  <p>I also took a peak at <a href="http://code.google.com/p/origami-pdf/" rel="nofollow noreferrer">http://code.google.com/p/origami-pdf/</a> , but this seems a bit harsh for a supposingly "simple" (at least in concept) task.</p>
  
  <p>Any ideas/suggestions?</p>
  
  <p>Thank you</p>