Go into SETTINGS - GENERAL - Keyboard and turn off "Auto-Corrections". This seems to disable it on all my apps.
It also disabled spell check when I did it.
Also is there a way to cursor back to the place where an error is located and correct it? Even when I make the font larger and use a stylus, the cursor will position itself at the end of a word and want you to delete the entire word, not just the one wrong letter in the middle. Once in awhile it will do it right, but not very often; and, I have not been able to figure out why that happens, either.