$pdf = PDF::API2->new();
    $pdf->mediabox('A4');
    ...
    $pdf->saveas('our/new.pdf');

    $pdf = PDF::API2->new();
    $pdf->mediabox(595, 842);
    ...
    $pdf->saveas('our/new.pdf');

    $pdf = PDF::API2->new;
    $pdf->mediabox(0, 0, 595, 842);
    ...
    $pdf->saveas('our/new.pdf');