title: Reference to System.Windows.Forms
body: <p>I'm using C# to command something in Excel but when I type</p>
  
  <pre><code>using System.Windows.Forms
  </code></pre>
  
  <p>it's not recognized by Visual Studio
  When I added the reference, I have this error message</p>
  
  <blockquote>
    <p>A reference to 'System_Windows_Forms' could not be added.
    The ActiveX type library '...' was exported from a .NET assembly and cannot be added as a reference.
    Add a reference to the .NET assembly instead</p>
  </blockquote>
  
  <p>Do you have any solutions?</p>