title: Copy DataTable to DataTable keeping the PrimaryKey
body: <ol>
  <li><p>I need to copy <code>dt2</code> into <code>dt1</code> but I can't use <code>dt1 = dt2</code> because <code>dt1</code> has a primary key while <code>dt2</code> does not. What's the best way to do this?</p></li>
  <li><p>Is is possible to add a primary key to an existing dataTable which is not empty?</p></li>
  </ol>
  
  <p>Thanks</p>