title: Switch active view between two Revit Documents
body: <p>I have a doc that is already opened in revit. A C# addin is activated and a form(modal?) is opened. A button event is then implemented to open a doc to transfer some mass elements from that file and document to the already opened document.</p>
  
  <pre><code>//the rvt file containing the mass elements opening code.
  Document doc = app.OpenDocumentFile(UserRVTFilePath);
  </code></pre>
  
  <p>I then would like to switch the active document back to the first opened document. Is there a Revit API method that exists to achieve this?</p>