title: how to get total number of pages in PdfQuery
body: <p>I'm trying to get how many pages a PDF has.  My attempt was to do this:</p>
  
  <pre><code>   pages = pdf.doc.catalog['Pages']
     print pages
  </code></pre>
  
  <p>but this prints <code>&lt;PDFObjRef:2&gt;</code>.</p>