Does VC due diligence involve revealing trade secrets?

An investor may desire to see anything he, she, or it wants before investing. There are measures you can take to protect your intellectual property - NDAs, patent, trademark, and copyright filings, etc. - but if you are relying on trade secret protection to protect software functionality, you may have a different problem.

VCs and other professional investors are generally not in the business of "doing business;" rather, they are in the business of investing in businesses and having them "do business." As a VC, I would expect any company in which I might invest to take all steps available in protecting whatever IP they have and I will want to know precisely everything about the company before I invest. VCs and other professional investors are less likely to execute NDAs (they would be bound by a mountain of conflicting contractual restrictions if they did so for each potential deal), so disclosure may simply be a risk you must take. That doesn’t mean you have to be UNprotected, it just means you most likely cannot lean on what may be inappropriate trade secret protection.
It would be very prudent to speak with an IP attorney in private to review the technology you have and how you many best protect it in contemplation of potential investment and, moreover, simply doing business.