combining pdf have issues

Hi all,

I need to combine pdf's using invoke DDX.

I tried it but I did't get the result.

Can anyone tell me how to combine pdf.

Here is the DDX details

<?xml version="1.0" encoding="UTF-8"?>
<DDX xmlns="http://ns.adobe.com/DDX/1.0/">
    <PDF result="out.pdf">
        <PDF source="in1.pdf"/>
        <PDF source="in1.pdf"/>
    </PDF>
</DDX>

When I place the 2 pdfs in Input folder, the result was the same 2pdf's.

Shaji