This page should answer your immediate customization questions.
Q1: Can all the code be run in the client's Azure environment?
A1: Yes it can. The subscription product offering currently runs the PDF editing process in our hosted environment and saves the PDF file to the client's SharePoint environment. That would be seen as a custom job and would bypass our subscription process. Speak to sales via the chat for pricing on private hosting in your Azure.
Q2: Can there be customizations to this product?
A2: Yes. Speak to sales via the chat to schedule a discovery call on your requirements. Our services are very affordable, and we are open to your thoughts and roadmap ideas - in some cases providing substantial discounts.