IDOC documents for Harvard

The deadline is the coming 3rd march…and i have to submit thre documents. Out of these three one is the federal tax return for 2015.

DO internationals also have to provide Federal tax return?
or can we provide our home country’s tax return?

Also how important are these documents as i have already submitted CSS profile which largely accounts all of such financial matters?

You provide the tax return your parents filed in their country.