I’ve created a process to convert XDP files into dynamic PDF (RenderPDF) in LiveCycle ES2. However, when I open the resulting PDF in Reader Extensions (to extend the form manualy) I get the following error message: "This document appears to be invalid. It can not be opened for processing."
It was not so much the number of fields but the filesize of the PDF. I'd suggest two courses:
1) Try adding an image to the form to take up some space and see what it does
2) Think about logging a support case so that someone can take a look at this.