Question

Why don't paper attract pen if pen is dropped on the paper according to newton's third law

Answer 1

it is due to static electricty. As you rub the pen in your hair electric charges (electrons) move around between the two, accumulating onto the pen.
When you place the pen over the paper, the excess electrons on the pen attract charages on the paper and when positive and negative charges come close, they grab each other and the paper sticks to the pen.
so it's all about tiny charges flying around and interacting with each other.

Answer 2

yes the pen attracts the paper but their mass is so low that the force of attraction is low that there is no movement at all.

thanks for asking