When you type text into any reasonably modern word processing program, even though your keyboard key shows that ubiquitous ASCII double quote symbol, you see nice “curly” opening and closing punctuation marks when you hit it. These special quotes can’t be found on your keyboard. But word processing programs understand that when you put something in quotes, you want nice left and right quotes, and it replaces the characters you typed in with the correct ones. The same goes with apostrophes.
DesignFestival: Special Entities of HTML