API Integration to generate PDF
I can't comment on the whole implementation, because I know very little about your requirements.
If you're not familiar with reports in F&O, forgot web services and such things for a moment and focus on reports. You'll need to decide whether it meets your requirements or not. If so, create a simple report working as a proof of concept. Let us know if you struggle with get it done.
When you know that you want to use a report and you have one, we can start talking about how to call it through integration.