It works
var tip = "<p>Most computers will open PDF documents automatically, but you may need to download <a title='Link to Adobe website-opens in a new window'";
tip +=" href='http://www.adobe.com/products/acrobat/readstep2.html' target='_blank'>Adobe Reader</a>.</p>";
if($("div#maincontent a[href*='.pdf']").length>0){
$("div#maincontent").children(":last-child").after(tip);
but it not
var tip = "<p class="adobe-reader-download">Most computers will open PDF documents automatically, but you may need to download <a title='Link to Adobe website-opens in a new window'";
tip +=" href='http://www.adobe.com/products/acrobat/readstep2.html' target='_blank'>Adobe Reader</a>.</p>";
if($("div#maincontent a[href*='.pdf']").length>0){
$("div#maincontent").children(":last-child").after(tip);