title: Regex for string containing one string, but not another
body: <p>Have regex in our project that matches any url that contains the string 
  "/pdf/":</p>
  
  <pre><code>(.+)/pdf/.+
  </code></pre>
  
  <p>Need to modify it so that it won't match urls that also contain "help"</p>
  
  <p>Example:</p>
  
  <p>Shouldn't match: "/dealer/help/us/en/pdf/simple.pdf"
  Should match: "/dealer/us/en/pdf/simple.pdf"</p>