title: The PDF viewer 'Evince' on Linux can not display some math symbols correctly
body: <p>I use <em>Evince</em> to view PDF files on Ubuntu Linux 10.04. But sometimes the program can not display math symbols correctly. </p>
  
  <p>An example. The PDF file can be download from:</p>
  
  <ul>
  <li><a href="http://jmlr.csail.mit.edu/papers/volume12/zhang11a/zhang11a.pdf" rel="noreferrer">http://jmlr.csail.mit.edu/papers/volume12/zhang11a/zhang11a.pdf</a></li>
  </ul>
  
  <p>See equation (1).</p>
  
  <p>On Windows, the equation is correctly displayed by Acrobat Reader:
  <img src="https://i.stack.imgur.com/ZZsE1.png" alt="enter image description here">
  But on Linux, the <code>\sum</code> is displayed as a solid dot:
  <img src="https://i.stack.imgur.com/ti5y8.png" alt="enter image description here"></p>
  
  <p>I have already installed packages: <code>ttf-symbol-replacement</code>, <code>libpoppler5</code>, <code>poppler-data</code>.</p>