Are you familiar with The Chicago Manual of Style? Hint: it doesn't provide the rules of etiquette while dining in the Windy City.
If you can't identify this book, chances are great that you won't be able to edit your work to the satisfaction of the publisher you are trying to impress or the employer whose company you are trying to land a job with.
Even if your aspirations aren't that high, what you say, says a lot about you and your company. Handing out a brochure or business card with misspellings, grammar mistakes or just mistakes in general can really ruin that first impression.
FACT: Most people can't edit their own work. Their mind "sees" the word on the page as they intended to write it, not how it actually appears. That is just one of many reasons why you need someone else to edit your work. So call in the professionals today.