title: pdf.js default viewer doesn't show pdf file
body: <p>I'm using pdf.js library with the recommended default settings:</p>
  
  <pre><code>&lt;iframe src="https://myserver.tld/lib/pdf.js/web/viewer.html?file=https://myserver.tld/generator.php?id=1" width="800px" height="600px"&gt;
  </code></pre>
  
  <p>So basicly I use a self-hosted verion of pdf.js and want the default viewer to display a pdf file which is generated by a php-script (<a href="https://myserver.tld/generator.php?id=1" rel="nofollow noreferrer">https://myserver.tld/generator.php?id=1</a>). </p>
  
  <p>It works fine to direct download the pdf file by typing <a href="https://myserver.tld/generator.php?id=1" rel="nofollow noreferrer">https://myserver.tld/generator.php?id=1</a> in the browser. </p>
  
  <p>Using this example: <a href="https://mozilla.github.io/pdf.js/examples/" rel="nofollow noreferrer">https://mozilla.github.io/pdf.js/examples/</a>  and rendering the page with a canvas element also works fine.</p>
  
  <p>But the prestyled viewer.html just returns</p>
  
  <pre><code>PDF.js Version 2.0.943 (build: dc98bf76)
  Nachricht: Invalid PDF structure
  </code></pre>
  
  <p>Does anybody know how to fix this issue or can provide a good, prestyled pdf viewer running in the browser? I dont want to style all the buttons, function etc on my own. Thank you</p>