[рони]

<a href="/kv.php"></a>
<div class="pdf" style="width: 100px;"></div>
<div class="pdf" style="width: 200px;"></div>
<div class="pdf" style="width: 300px;"></div>
<div class="pdf" style="width: 400px;"></div>
<div class="pdf" style="width: 5px;"></div>

<script>
var o = document.getElementsByClassName('pdf');
var max=[].reduce.call(o,function(a,b) {
   return Math.max(a, b.scrollWidth)
},0);
alert(max);

</script>