问与php集成的wkhtmltopdf不工作

EN

<?php
echo exec('whoami');
$cd = "cd C:/www/genpdf";
exec($cd);
$command = "C:/Program Files (x86)/wkhtmltopdf/wkhtmltopdf -O landscape C:/www/genpdf/index-5.html C:/www/genpdf/index-5.pdf";
exec($command);

if (file_exists("C:/www/genpdf/index-5.pdf")) {
header('Content-type: application/pdf');
header('Content-Disposition: attachment; filename="index-5.pdf"');
readfile("C:/www/genpdf/index-5.pdf");
}

else {
    echo "error";
}