Depends on where you live and on the dealer involved.
In my state the documentation fee is fixed, by the state, at $35, and all new car buyers pay it. It is to cover the documentation work by the dealer to register the vehicle title, and change your title over to you when the vehicle is paid for.
Some states have higher recommended fees, some have no recommendations, many allow dealers to charge whatever they want to and call it 'documentation fees.'
In many cases, ridiculous documentation fees are merely a 'hidden' source of extra profit for dealers who want to play those games. Sadly, many do.
I paid a mandated documentation fee of $35 when I bought my new xB.
My total invoice was posted price of the xB, state tax, license, and documentation fee. The dealer did not add any cute "profit" fees to the cost.
YMMV,
Tomas