They can open up lines of credit in your name, for more than you can count.
They can open health care coverage and get health care- including any hugely expensive procedures- in your name, so you have none.
You name it, they can steal it. If your documents have been mispplaced or stolen, call all of the credit bureaus immediately, your bank, your health care insurance company, Social Security, and the IRS. And report it to police.