ok the iPad does have Siri built in and works very very well, just enable Siri in the settings on your iPad and then touch the icon on the keyboard that looks like a microphone.
there is also dragon naturally speaking a free app Dragon Dictation by Nuance Communications
Both Siri and the above app work best when you speak clearly with no hesitation , so if you feel an ‘um’ or ‘erm’ etc coming on stop the dictation and gather your thoughts
I find both the systems work very well for people of hard hearing and those who are unable to write or spell the way they would like to be able.
This entire blog has been done by me talking to Siri