@JR here’s the steps I would take:
1. Download the PDF template and then customize it to include the fields that you need and save it to the file cabinet.
2. When you load the record like you do you can create a JSON object and populate it with the fields you need that correspond to the placeholders on your PDF xml template.
3. Grab the assemblyitem field from the workorder record and load that to get the assembly item values you need and add those fields to your JSON object.
4. You would now have a placeholder in your PDF xml template and the JSON data to match.