To be a patent engineer, you must have a college degree or above in science and engineering. It's not very interesting to be a patent engineer in an enterprise, because most enterprises don't attach importance to patent engineers, and only think that they are handyman employees, which is quite boring. If you want to engage in patent work, you still have to get a good patent agent qualification certificate first, and then you can work in a patent agency before you can develop, otherwise it will be really boring.
Purchasing depends. If you are the head of the purchasing department, it's not bad, otherwise you have a lot of errands and it's quite hard.