looping through "move_uploaded_file" files

Question

I am trying to upload multiple pdf files into my website's folder. It uploads only the first pdf from the pdfs, so I am trying to use an array, but it gives an error.

$target = "../media/covers/".basename($_FILES['image']['name']);
$pdf_target = "../media/pdfs/".basename($_FILES['pdf_file']['name'][0]);
// I use [0] above to access the string

foreach($pdf as $idx){
        if (isset($_POST["upload"])) {
            if(move_uploaded_file($_FILES['image']['tmp_name'], $target) 
            && move_uploaded_file($_FILES['pdf_file']['tmp_name'][$idx], $pdf_target)){
                $msg = "image uploaded";
            }  else {
                $msg = "There was a problem uploading image";
            }
        }
}

I expect all files to be uploaded to the folder "../media/pdfs/"