Editing and proofreading sit at opposite ends of the revision process. Editing happens while your document is still evolving: an editor improves sentence structure, flow, consistency and clarity.
Proofreading is the final polish. A proofreader corrects typos, punctuation and formatting slips once the content is final.
Rule of thumb
If you are still making changes, choose editing. If you are about to publish or submit, choose proofreading.