Always run your important documents through a spell checker. It will plane lee mark four you're revue, miss steaks ewe mite knot sea. However, it probably won't do much for poor grammar or sentences like that one! Linux has a rudimentary spelling checker, which you can invoke like this:
spell important.txt Perform a regular spell check on important.text.
spell -b important.txt Perform a spell check using British spelling rules.
If the spell checker finds words that do not appear in its dictionary, it will display them on the console