Even routine documents should be checked for accuracy, although most correspondence and internal materials can probably get by without formal proofreading. But anything destined for a wide or critical audience will benefit from careful, professional proofreading — mass-produced and long-lived documents (such as advertisements, brochures, annual reports, and manuals) should receive at least two passes. Consider the sensitivity level of your material as well. Certain erroneous facts and figures are not only embarrassing but dangerous.
The proofreader’s responsibility is to correct misspellings, faulty grammar, typographical errors, and inconsistencies in format and style. Common facts and references will be verified.
Copy-editing is a wise choice for communications that are unclear, verbose, overly technical or stilted, outdated, or disorganized. It’s especially helpful as a way of unifying collaborative work that’s been written by more than one author.
The copy editor is responsible for improving rough text with editorial refinements. In some cases this includes restructuring and reorganizing, but not extensively rewriting. Superfluous material and unnecessary or confusing details may be cut, but the writer’s voice will remain recognizable.