If you used MPDF as your library then add this function to your themes' template.php:
function MYTHEME_print_pdf_mpdf_alter(&$mpdf, $html, $meta) {
//return;
if(is_view_path()) {
$paper_size = variable_get('print_pdf_paper_size', PRINT_PDF_PAPER_SIZE_DEFAULT);
$format = $paper_size . "-L";
// set document information
$mpdf = new mPDF('UTF-8', $format);
$mpdf->SetAuthor(strip_tags($meta['name']));
$mpdf->SetCreator(variable_get('site_name', 'Drupal'));
}
}
I could not find a way to alter the paper orientation after the object was instantiated, so I opted to just create it again (orientation is set in class creator).
You should then implement a function called is_view_path
that returns true if it detect the printpdf path of the view, so that the code only runs for your specific view.
function is_view_path() {
$path = current_path();
return $path == 'VIEWPATH'; // just add your view path here
}
If you used TCPDF you should look at the function print_pdf_tcpdf_print_pdf_generate in print-pdf-tcpdf.page.inc at how to instantiate the $pdf object, and then implement an alter hook similarly to what I did above. I could not do it as for some reason I cannot get the tcpdf library to detect.
For DOMPDF I could not find an alter hook.