Although the terms are used interchangeably by many; editing and proof reading are two different tasks which require full concentration and requires focusing on different aspects of writing. Editing requires concentrating on content, structure, style, citations. Proof reading may be said as final stage of editing which concentrates on grammatical and spelling errors, punctuation, typography etc. While proof reading can be done by any person editing really requires a professional. Editing requires critical thinking and proof reading requires concentration and attention to details.
Editing requires checking for the logical flow, consistency, clear expression of the idea, and clear message to the target reader. The purpose of the writing should be clear throughout the text, maintain logical flow from one paragraph to other, should not have or repeat unnecessary words etc. All this will be taken care during editing whereas proof reading typically checks for grammatical and typography errors. Reading the report twice or more helps in finding the grammatical errors. Typographical errors can be spotted while reading backwards. Some of the typographical errors include double spacing, misaligned margins or tables, incorrect capitalization, inconsistent bullet points, wrong number sequence etc.
Editing requires following a citation style prescribed by the writer or university or some publishing house. There are few writing styles like MLA, APA Harvard etc which are used based on the type of work. A professional editor must have experience with all kinds of styles and a proof reader really need not worry about this. It is better if the editor is also aware of the technical matter like typesetter or printer, web design or printing etc although they are not mandatory. Selecting an editor and proof reader depends on the kind of work and sometimes a single person can accomplish both the tasks while at times different persons may be required.