What can I receive from a doctor as a disabled person that I could show potential employers?

Disabled Documents. I'm not sure you need to show potential employers anything, since this would imply discrimination on the basis of your disability and that is against federal law. If you're trying to explain your limitations because of your disability, that would seem proactive on your part and i'm sure a prospective employer would appreciate your disclosure. First be sure the job is something you can do.
A letter. You can receive a letter from your doctor outlining what your disabilities are and how they may or may not affect your ability to do your job. You may need to see a specialist in occupational medicine if your personal doctor is not qualified. Expect to pay for this service as insurance companies will not. Good luck.