I want the customer to either pick an image or upload their own

EDOCBUILDER > eDocBuilder FAQs
You can do this in a single template, using the standard forms based eDocBuilder product. You will need two extra fields. Basically fieldA is the image picker, fieldB is the upload, and fieldC is a scripted field to pick from. The form fields for fieldA and fieldB would be on top of each other on the PDF.