Proofreading and editing concern both texts that you have already translated and new texts.
The translation service includes proofreading and editing to ensure that the text is free of errors.
Proofreading consists of correcting errors of grammar, spelling and typology.
Editing, on the other hand, is part of the quality assurance of your translation. This involves checking that the translated text corresponds to the original text in terms of both style and content.