Let me structure the response: start with a refusal to provide the key, explain why, then offer legal alternatives. Keep it friendly and helpful. Make sure the user knows I can't assist with illegitimate methods but can point them in the right direction otherwise.
First, I know that providing or requesting activation codes is against most terms of service and can be illegal because they're meant to be licensed. So I need to make sure I don't give them a key or tell them how to obtain one. But maybe they're looking for alternatives.
They might be a student or small business user who can't afford a full license. In that case, suggesting they check for educational licenses or free trials could be helpful. Also, recommending legitimate sources like the official website or authorized resellers is important.