title: Timed file encryption with pdftk
body: <p>I know that I can "encrypt" a pdf file using pdftk and the following command: <code>pdftk mydoc.pdf output mydoc.128.pdf owner_pw foopass</code>. This I find disables printing. There are other options available that allow for low quality printing etc.</p>
  
  <p>However, I'd like to encrypt a pdf in such a way that after say, 14 days, it cannot be opened anymore without a password -- a timed encryption, if you will, with unix command line tools or some script that would do the trick for me.</p>
  
  <p>Any comments? Suggestions?</p>
  
  <p>I am doing this because I teach an undergraduate class and am required to upload homework problems and solutions. I believe students create dossiers out of such pdfs for future students to use and cheat. No, I cannot print pages and then share it with them.</p>