title: Access the active Excel workbook using OpenXML and C#
body: <p>I'm trying to manipulate an Excel spreadsheet in C# using OpenXML.  Specifically, I would like to access the currently active workbook that is open.  I've only been able to find examples that open up an Excel document <em>given a filename</em>, such as:</p>
  
  <pre><code>    using (SpreadsheetDocument myWorkbook =
  SpreadsheetDocument.Open(filename, true))
  </code></pre>
  
  <p>(Note: Using the 'Microsoft.Office.Interop.Excel' way, the active workbook is accessed like:
  <code>Workbook activeWorkBook = (Workbook)Globals.ThisAddIn.Application.ActiveWorkbook;</code>)</p>
  
  <p>Has anyone done this?</p>