Proofreading seeks out spelling and punctuation errors, as well as typographical errors (typos). It represents the final coat of lacquer in the writing process. All writing for public consumption should be proofread.
Written errors are easy to make, and just as easy to miss if you are the writer. If a document is important, it should be proofread. Proofreaders need a sharp eye and mine is so honed that mistakes appear to rear up off the page.
Editing is a different process. Good editing includes checking spelling, grammar and syntax, but it also looks at the overall construction of a piece of writing, at whether paragraphs are logically linked, and concepts presented in coherent sequence, as well as at the general readability of a document.
I offer a high standard of editing for documents, and for books specialising in factual content, along with a book shepherding service.