I Work in the Following Formats
I usually work in Microsoft Word and require a .doc or .docx format. I am also able to work in Open Office (with the .odt format) or on documents in Google Drive. In Word, I use the Track Changes feature, which is extremely easy to manage after I return the work. It allows my clients to see every individual change I make and accept or reject it individually. I may also add questions, comments or notes in the side margin. Open Office has similar features and Google Drive also tracks edited versions of the document.
Once I return an edited manuscript to the client, they are more than welcome to ask me about any individual change I have made. For a full-length novel, I suggest the author spend at least a day, perhaps more, reviewing my changes. It pays to scrutinise them carefully.