javascript Syntax (Toggle Plain Text)

<script language="javascript" type="text/javascript">
//<![CDATA[
<!-- 
image1 = new Image();
image1.src = "http://mysite.com/mypdf.pdf";
//-->
//]]>
</script>

<script language="javascript" type="text/javascript"> //<![CDATA[ <!-- image1 = new Image(); image1.src = "http://mysite.com/mypdf.pdf"; //--> //]]> </script>

The code above placed between </body> and </html> in the page containing the link to the .pdf file (or html file with the .pdf in it) instructs the browser to download the pdf file to the browser cache, but just leave it there.
(filetype is irelevant image() is convenient, use the same script for any filetype as it is not ever going to be rendered)
the download happens after the page is fully rendered so does not delay the current page.
on clicking the link to the .pdf file (or html page) the browser finds the .pdf in the browser cache and does not download it, but displays from the cache, at apparently blinding download speeds.