title: DocumentFormat.OpenXml.Packaging add as a reference
body: <p>I try to add the <code>DocumentFormat.OpenXml.Packaging</code> reference in <code>Visual Studio 2012</code>. But if I go to "Reference" > "Add reference" there is not reference like this. I was googling the whole evening but still don't find it. Often I saw that I have to look at ".NET" tab in references. But there is no tab called ".NET". Can someone please help me to get out of this dumb situation?</p>
  
  <p>Thanks!</p>