publishing - Is it better to save each chapter in a separate word document or all in one document?

I'm new here.

In the past, I've written countless articles for newspapers, and I almost never needed to edit more than a page or two. However, I have agreed to edit an entire (existing) novel for its second edition/re-print.

I'm planning to use MS Word for this.

Is it better to re-write/edit each chapter in a separate word document or is it better to save everything to one file?

I plan on editing 1-2 chapters per day, which roughly equals 10-12 pages. There's a total of 502 pages in the book.

Thanks in advance for your help and advice.

PS: The book will be available in both paper and electronic formats.