Hi,
I specialize in creating custom-made scripts for PDF files, and in fact I've already developed a tool that does something similar to this (it populates a PDF using URL parameters)... Can you share the JSON file (it's not attached to the project), and explain a bit how you want it to work, exactly? Where is the JSON file going to be located, and how should the script load it when the PDF is loaded?
Regards, Gilad (try67)