As some of the answers below mentioned, VCs and angels generally won’t sign a non-disclosure agreement (NDA). If they were to sign NDA’s from every startup whose idea they were looking at, it would kill their business model. They would literally be buried in hundreds of NDA’s, and spending a ton of money on attorneys to advise them on the NDA’s.
Generally, product ideas are not protectable by patent law. However, you may be able to patent a specific way of doing business, with a utility patent. A utility patent covers a new and useful: Process, Machine, Article of manufacture, Composition of matter, or any new and useful improvement of these. It’s possible to file a provisional patent on your own, however, if your product/platform/app changes, you would incur additional legal fees because you’d have to change the patent application.
The bottom line is that you probably should build a prototype before going to investors, and meet with a patent attorney to see if your idea is something that is patentable.
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