title: How to add a hidden image to a PDF document?
body: <p>I have a program. It outputs to pdf, but that is close to impossible to read from again. So i need a additional file attached to my PDF in order to be able to make it editable in my program. Attaching a file to PDF is a good idea, but that is visible to the user, which i don't wan't it to be.</p>
  
  <p>An alternative is to hide my readable file format inside an image which would be added to the PDF somewhere to the top of the first page, before everything else... Even to metadata if that's possible...</p>
  
  <p>That way I can extract image from pdf using a PDF library (iText), and read from it.</p>
  
  <p>My question is how to add image to PDF to be as well hidden as it could be (visually and by accesibility). And it has to be in a place which would be same for any created document (somewhere on the top, or on the very bottom of the document, or to the part of the document which isn't displayed at all... I'm really guessing here, I'm not really familliar with PDF file format)...</p>
  
  <p>Any ideas?</p>
  
  <p>P.S. It's not really important which image is it, I could be a e.g. completly transparent image, 1x1 pixels.</p>