During editing, an editor will make changes and offer suggestions in order to improve the overall quality of the writing. The goal of the editor is to improve the fluency, the consistency, the accuracy and the overall readability of the writing.
Proofreading is not as thorough and is a cheaper service. It's still an important part of the process. The proofreader will mostly focus on general language mistakes such as grammatical, spelling, and punctuation errors.
