title: Get all opened Excel-documents
body: <p>I need create xls-file with own data. But file may already be created, and opened by user.</p>
  
  <p>(1) If file not exist:
  new ApplicationClass()
  Workbooks.Add()
  SaveAs()...</p>
  
  <p>(2) If file exist and not opened: not problem - goto (1)</p>
  
  <p>(3) if the file exists and is opened by the user: need find it workbook and reform data of worksheet.</p>
  
  <p>With (3) I have problem. Marshal.GetActiveObject("Excel.Application") finded only active workbook.</p>