When interns join the company, the company needs interns to provide copies of their ID cards and household registration books. Is it reasonable and formal, and is there any risk?

Generally, new employees in more formal companies need to provide copies of their ID cards and household registration books before they can go through the entry procedures. If some companies don't need these things, then you may want to consider the credibility of this company. Generally speaking, providing these two copies is risk-free and reasonable and compliant.