I have used a non disclosure agreement in the past when showing some of my ideas to different companies. A non disclosure form is a document which you will ask a company to sign before you show them your idea. By signing they are agreeing not to disclose it to anyone else (without you agreeing to it). It also gives you the proof that you have shown them your idea.
Not every company will agree to sign a confidentiality agreement for fear that they may already be working on an idea similar to the one you are about show them which would cause a conflict. I recently was listening to a podcast where a toy company owner was interviewed, she said that they never accepted ideas from outside the company for fear that either
a) They may already be working on something similar
b) Your idea may (even innocently) influence a future idea.
If you are looking for somewhere to find a legitimate sample non disclosure agreement you can find one at