How to add a custom block on Print module?
You can do this by using Display Suite module. It allows you to add the block as a field in the "Manage display" tab of your content type. You can then place it wherever you want on your node page.


  Display Suite allows you to take full control over how your content is
  displayed using a drag and drop interface. Arrange your nodes, views,
  comments, user data etc. the way you want without having to work your
  way through dozens of template files. A predefined list of layouts (D7
  only) is available for even more drag and drop fun!