title: How to read .xls/.csv document using DocumentFormat.OpenXml.Packaging.SpreadsheetDocument class?
body: <p>How to read .xls/.csv document using <code>DocumentFormat.OpenXml.Packaging.SpreadsheetDocument</code> class?</p>
  
  <p>Can read <code>.xlsx</code> file perfectly. But having <code>FileFormatException</code> in this line when xls file is given.</p>
  
  <pre><code>_spreadsheetDocument = SpreadsheetDocument.Open(FileStream, false);
  </code></pre>