You can change the panel's html content to switch the pdf files.
<div id="p" class="easyui-panel" title="Panel" style="width:700px;height:300px;padding:10px;">
<embed width="800" height="600" src="test.pdf"></embed>
</div>
Call this line to change the pdf content.
$('#p').empty().html('<embed width="800" height="600" src="test2.pdf"></embed>')