You will need a third part app or a link to one that does it for you.
There are several free ones but they usually put an ad(s) on your page.
CoffeeCup had a decent one for about $34. I use WrenSoft. They have a
free version (includes an ad), a medium version (will scan 100 pages and
I think 500,000 unique word) and a pro model (bunches and bunches of
pages and words). I use the medium version which cost $49.