An option is to send pdf data to iframe
<form action="your_pdf_handler" method="post" target="pdf-iframe" id="pdf-form">
<!-- your post data here -->
<input type="hidden" name="foo" value="bar" />
</form>
<iframe name="pdf-iframe" src=""></iframe>
and then submit the form using jQuery
$("#pdf-form").submit();
Alternatively, instead of echoing pdf data, you could save the generated pdf on your server and return its url in a json response:
{
"pdf_url": "/pdfs/my_document.pdf"
}
and then use jQuery.post() like this:
$.post("your_pdf_handler", {your: data}, function(data){
window.location.href=data.pdf_url;
});