test.cs

[HttpPost]
public HttpResponseMessage LoadDocument(string ConnectionID)
{
  // connect the WebSocketHandler with the ConnectionID
  WebSocketHandler wsHandler = WebSocketHandler.GetInstance(ConnectionID);

  // the document directly server-side
  wsHandler.LoadText("Documents/demo.tx", StreamType.InternalUnicodeFormat);

  return new HttpResponseMessage()
  {
    StatusCode = HttpStatusCode.OK
  };
}