title: Error when getting the Title list of all content controls in the shape (Word)
body: <p>I want to get the Title of all content controls contained in word document (shapes). I found out some tips on the Internet. But when I run this code, it has an error (in the picture)</p>
  
  <p><a href="https://i.stack.imgur.com/OZBM9.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OZBM9.jpg" alt="enter image description here"></a></p>
  
  <pre><code>Microsoft.Office.Interop.Word.Application oWord = (Microsoft.Office.Interop.Word.Application) w;
  _activeDoc = oWord.ActiveDocument;
  foreach(Microsoft.Office.Interop.Word.Shape s in _activeDoc.Shapes)
  foreach(Microsoft.Office.Interop.Word.ContentControl cc in s.TextFrame.TextRange.ContentControls) {
      MessageBox.Show(cc.Title.ToString());
  }
  </code></pre>