Proof reading of manuscript: This is the essential finishing touch to be carried out on a final draft before placement into design software for print or converted to e-pub. Here, the editor is checking for spelling, grammar, typos, etc. This is essential for all manuscripts before their placement into the public arena, and is usually done by an external professional who has not previously worked on the manuscript. When the book has been placed into the design template, the author will need to check through themself and sign off on the final version.
Proof reading of a scan: After a document is scanned and converted into text, it must always be properly proofed and checked, since the optical recognition of the characters from the scan (which is an image) will never be 100% accurate. Depending on the condition of the original book, it may be a straightforward job, or it may take longer (a cramped, faded or mottled original often creates extra punctuation and distorts spelling), as extensive corrections may be needed. Again, when the book has been placed into the eBook format, the author will need to check through themself and sign off on the final version.