How to create a text field within a DDX file?

Question

I'm trying to create an adobe form that consists in a text field inside a DDX file that contains properties such as watermarks and other options.

Adobe DDX reference indicates that it supports XDP declarations but I've not been able to make it work.

What I'm trying to accomplish is that every time a user opens a PDF a text field should populate with the current Date and time. I already created a javascript that will be attached in the PDF from the DDX but it's failing in the instruction this.getField("NAME_HERE") because it doesn't exists.

My last attempt was to define a XDP field but it's not recognized since XDP is not bound.

<PDF result="onlyPrinted" return="false">
    <XDP>
        <!--<XDP:field name="onOpenJS"/>-->
    </XDP>
    <JavaScript name="getDate" source="File:///PATH"/>
    <PDF source="mainWatermark">
    </PDF>
</PDF>

Have you ever created a form in a DDX file?