OK Robert, I'm still a little peeved that you didn't
answer my question sometime back about what speed
reading course you would recommend? You did take a
speed reading course didn't you? May be you didn't
see my question.
Anyway, the solution you're after:
Go to Tools -> Autocorrect
Then either:
1) Deselect "Replace text as you type"
or
2) Scroll down to replace "acn" with "can"
and delete this line.