title: flask render_template with url parameter
body: <p>I use pdf.js to render pdf in web. The format of the target url like this:</p>
  
  <pre><code>http://www.example.com/book?file=abc.pdf
  </code></pre>
  
  <p>My problem is:
  I use flask template to generate page using:</p>
  
  <pre><code>return render_template('book.html', paraKey=paraValue)
  </code></pre>
  
  <p>But how to attach url parameter "file=abc.pdf" to url?
  The parameter will be read by viewer.js(included in book.html) that uses it to read file for rendering pdf.</p>
  
  <p>I'm new to flask, hoping guys giving me some help!</p>