Hi,
i was experiencing the same problem when trying to export a excel document to pdf in landscape mode using mPDF. I'm using PHPEXCEL 1.7.8
I have found a workaround, but you have to modify the mPDF.php file in the directory PDFPHPExcel\Writer\PDF at line 110.
The original block of code is:
$pdf = new mpdf();
$pdf->_setPageSize(strtoupper($paperSize), $orientation);
$pdf->DefOrientation = $orientation;
The modified (working) block of code is:
$pdf = new mpdf();
$ortmp = $orientation;
$pdf->_setPageSize(strtoupper($paperSize), $ortmp);
$pdf->DefOrientation = $orientation;
$pdf->AddPage($orientation);
it seems like the problematic line is the setPageSize function line which overrides the chosen orientation.
I have not investigated further on the problem, and I know this workaround is not the ideal solution, but it works.
Hopefully the PHPExcel team will provide a better solution.
Regards