Spellcheck question

There's no such option in Acrobat. You can only run Spell Check on comments and fields.

If you want to run a spell-check on the static contents of the file you will need to use a script, such as this (paid-for) tool I've developed: https://www.try67.com/tool/acrobat-spell-check-suite

Notice that even with this tool you can't replace the old text with the new one automatically. It only marks up the misspelled words for you (and makes suggestions as to the correct spelling).