The easiest way to do this is through link targeting. Since it looks like your populating the links dynamically, you could simply create your link like this:
<a href="locationOfFileFolder/<?php echo $row_pdf['myfile']; ?>" target="_blank">Download PDF</a>
The trick is to set target to "_blank". Keep in mind, though, that some browsers will just force it to download if the browser does not have pdf reading capabilities.