Should I respond to emails (resembling spams) asking for my papers?

I don't even think this is for harvesting papers. My guess: it is to validate email addresses so that actual spam campaigns can achieve a better return on investment.

The worst case of responding is a little more spam, so I would respond. I often find myself in a culture slash between what I consider rude and students consider acceptable email behavior. It wouldn't surprise me if a number of students were prepping for an exam and all wanted your paper.

As for the paper phishing bot, it seems like it would be more efficient to use student library access to download papers (automatically) than to collect them via email.

The beginning and the end of your account contradict each other, so I do not understand if you got this message many times, from several different addresses, or once or twice, from the same person.

In the first case, it definitely seems a spam-like behavior.

In the second, it could be a honest message from a grad student with poor English knowledge. Check if the names are compatible with this explanation; if so, I would definitely answer. It could even earn you a citation. :)