NDA is not a substitute for a patent. Patents give you a solid proof of ownership of an idea or a product itself whereas an NDA is just a contract that is signed by two people who promise to keep things confidential. I read an example on a website that really helped me understand the difference so I’d like to share it with you. Let’s say you have an idea to develop something and you share that idea with person A and sign an NDA with them. If person A goes and makes your invention “as their own”, you can sue them and win. However, if person A goes and tells person B about the idea and they decide the make the invention, you can’t do anything about that since your NDA is only between you and person A. Patent is really the only way you can protect yourself fully.