<!-- The HTML Code inside of the IFRAME: -->
<embed src="path_to_script_which_generates.pdf" type="application/pdf" id="pdf"width="100%" height="100%"></embed>

<!-- JS Code (I would also put it inside of the IFRAME): -->

<script>
var doPrinting = (id)
{
    var pdfObject = document.getElementById(id);
    if (typeof(doc.print) === 'undefined') {
         setTimeout(function(){ doPrinting(id); }, 1000);
    } else {
        pdfObject.print();
    }
};

doPrinting('pdf');
</script>