I just finished academic research with real-world practical applications. I am thinking of presenting my project to companies, but I will love to know if it is advisable to patent my work, before contacting the companies or use an NDA instead? Should I file a patent myself?
It is highly desirable to protect your invention by way of a patent before taking it to the industry. NDAs (non-disclosure agreements) have serious limitations especially in a David and Goliath if you are approach a large company.
You need a prototype before you can patent your invention. A provisional patent is probably your best option and one filed by a patent attorney at that.
The trouble with provisional patent applications is that you will only generally find out about problems with them during litigation years down the track so getting a patent application professionally prepared is important to give it the best chance of survival.
I recommend against trying to self-file. I have not seen a self-filed patent that gave decent commercial protection in my 20+ years of practice.