It is always better to took for errors either in the chrome's console or firefox's firebug when things don't work for you. In your case if you had looked, you'd have seen 'Uncaught ReferenceError: jQuery is not defined', which means you need to use jquery for fancybox to work. Also you need to include jquery mousewheel and jquery easing along with fancybox.js.
Here's a working demo for you. http://jsfiddle.net/g36YD/7/
<p><a class="iframe" href="http://contents.tacticalasia.com/download/511-Tactical-Catalog-2012.pdf">Zero</a></p>
$("a.iframe").fancybox({
'width': 640, // or whatever you want
'height': 480, // or whatever you want
'type': 'iframe'
});