// THHO: MediaBox is always in Portrait mode (see Height, Width)
/*if (this.orientation == PageOrientation.Portrait)*/
  MediaBox = new PdfRectangle(0, 0, size.Width, size.Height);
/*else
  MediaBox = new PdfRectangle(0, 0, size.Height, size.Width);*/

if (this.orientation == PageOrientation.Portrait)
  MediaBox = new PdfRectangle(0, 0, size.Width, size.Height);
else
  MediaBox = new PdfRectangle(0, 0, size.Height, size.Width);

private static void HackPageRotation([NotNull] PdfDocument document)
{
    for (int index = 0; index < document.PageCount; index++)
    {
        var page = document.Pages[index];
        if (PageOrientation.Landscape == page.Orientation)
        {
            var value = page.MediaBox;
            var size = new XSize(value.Height, value.Width);
            page.MediaBox = new PdfRectangle(value.Location, size);
        }
    }
}

      internal override void WriteObject(PdfWriter writer)
      {
         // HACK: temporarily flip media box if Landscape
         PdfRectangle mediaBox = MediaBox;
         // TODO: Take /Rotate into account
         if (orientation == PageOrientation.Landscape)
             MediaBox = new PdfRectangle(mediaBox.X1, mediaBox.Y1, mediaBox.Y2, mediaBox.X2);