title: How can I invoke a dynamic external dll
body: <p>In C#, I want to call a method in an external DLL with signature <code>bool IsValid(string)</code>,
  but the name of the dll is coming from input as a string.</p>
  
  <p>How can I:</p>
  
  <ol>
  <li><p>Call the external method?</p></li>
  <li><p>Implement the <code>IsValid</code> method?</p></li>
  </ol>