I hold a master copy of the MS and the author responds to my editing (as well as providing his own amendments, additions and deletions) as email attachments of the transformed chapters fly between us. Just recently, long after the radical initial assaults on the MS were over, I discovered the perfect computer method for handling this.
Initially I saved the author’s latest chapters to a folder. To transfer his stuff I opened this folder and that containing the master copy and went cross-eyed moving from one chapter to the next incorporating his changes (helpfully marked in red). Since there are forty chapters much time was spent switching from one folder to the other.
Now I amend the file titles of his chapters with an X and save them direct to the master copy folder. The contents now look something like this:
Chapter One (Master file)
Chapter OneX
Chapter Two (Master file)
Chapter TwoX
I am thus always working in the same folder saving time and irritation and helping to cement the correct author/editor relationship. Another wheel rediscovered.