Proofreading involves correcting spelling mistakes, grammatical errors, incorrect punctuation marks, and lack of consistency in the text style such as fonts, highlighting (bold and italics), spacing, underscores, etc.
As a proofreader, my job is to read each document and check for consistency and overall layout of the information. Proofreading mainly focuses on ensuring that nothing has been missed during the copy editing process. Authors also use a proofreader to polish their finished product.
The process of proofreading does not involve re-writing or changing the form in which the document has been written. If you want more in-depth editing, you should consider purchasing copy editing.
Hiring a proofreader is particularly helpful if English is not your native language. Proofreading smooths out language errors, formatting issues, missing words, typos, punctuation errors, spelling, and formatting inconsistencies that can be difficult to notice if English is not your first language.