What's the difference between copyediting and proofreading?
A copyeditor deals with the manuscript before it is typeset. She makes sure the manuscript makes sense and reads well. Name and facts are verified, which may require that a copyeditor have some background in the subject the editing assignment covers. She looks for consistency in style, spelling, abbreviations, and numbers, making sure they comply with the publishing house standards.
A proofreader usually compares typset page proofs with the original manuscript to make sure that nothing is omitted, added, or changed. She also makes sure that the typesetter has followed specifications for typeface, style, and margins. The proofreader must be on the lookout for mistakes in the original manuscript as well.