title: Save desired pdf page from pdf file using ruby
body: <p>I have a pdf file. I want to save a given page (page #5, for intsance) as other pdf file. How do I accomplish this?</p>
  
  <p>So far I've used <code>pdf-reader</code> gem – but it's suitable for reading pdfs (though I can get to the page I want), and I gem <code>prawn</code> – this one's only for writing pdf (I can only create empty pdf file).</p>