When you’ve already had at least one copy edit — either by me or by another editor — and you’ve laid out your document (if it’s the sort of thing that requires laying out), it’s time for proofreading.
Proofreading is a lot like copy editing, but it’s more restrained. I look for clear errors of grammar, spelling, and punctuation.
But at the proofreading stage, I try to minimize changes. This limits the risk that an error will be introduced when it’s too late to catch it.
Because proofreading can be done on a document that’s already been laid out, it can include things like headlines in newsletters or chapter headings in books — things that may not be there at earlier stages.