I want to learn how to write pharmaceutical combination drug (API) patents and the format for them. Are there any good references also to learn how to evaluate the quality of a patent? whether it's good or bad?
You may want to check out ANDA Litigation at https://www.amazon.com/ANDA-Litigation-Strategies-Pharmaceutical-Litigators/dp/1634254589 Yes, the book is expensive, but it's also exhaustive. It talks a lot about the requirements for patenting pharmaceutical combination drugs.
As for evaluating the quality of a patent, there's two ways 1) prosecute and litigate a ton of patents to develop the necessary expertise or 2) look for patents which have been successful in asserting patent infringement and avoiding invalidation. They're high quality :)