Very little. At the angel/seed stage, they're investing in the founders, so there's no expectation of patents, etc... They might check that you're incorporated in good standing, and ensure you have a solid startup/corporate lawyer, and have good employment and IP ownership agreements with your staff and contractors, and that's about it.
The due diligence will be focused on these main areas: 1) product prototype, 2) team, 3) total addressable market and 4) operating model (i.e. use of proceeds).
Varies greatly due to company focus and product(s) and/or services contemplated, but diligence focus at this level is usually focused on product viability and market opportunity, competitive landscape, team and path to market.