title: PdfSharp does not change file system info
body: <p>I'm writing a program that changes the modification date of all files in a directory.</p>
  
  <p>I can apparantly change the properties, but not for windows to recognize it.</p>
  
  <pre><code>private static void ChangeDateTypeOfFile(DateTime date, string filepath)
  {
      int state = PdfReader.TestPdfFile(filepath);
      if (state != 0)
      {
          System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
          PdfDocument doc = PdfReader.Open(filepath);
          doc.Info.ModificationDate = date;
          doc.Save(filepath);
      }
      else
      {
          Console.WriteLine(state);
      }
  }
  </code></pre>
  
  <p>When I read the property before and after I change it I can see the difference and it seems to work. Yet in Windows File Explorer I can't see any changes (nor with <code>title</code> and <code>author</code> for example). And the last modified date changes to when I ran the code.<br>
  How can I persistently change this information?<br><br>
  Edit:<br>
  When I open it with Notepad I can see the line:</p>
  
  <pre><code>/ModDate(D:20070129000000+01'00') //Set the date to 2007
  </code></pre>
  
  <p>Why does the file Explorer not display this information?</p>