MS Word is kind of the standard for word processing (although I prefer a different one).
Teachers correct a lot of papers. They are worried about errors. Even though the research shows that correcting errors does little to improve student writing, teachers still do it. It makes them feel good, like they are doing something.
Instead of only giving feedback to one student, I collect all the written assignments in a Word Processor (students have to send their final version by email or similar). I erase all the names. I correct all the work, and hand it back to all the students. This works better if they have online access to the document, but usually, a first-year writing assignment you can fit about 5 or 6 onto one page.
By all means, though, leave the correction marks on their mistakes. To do this in MS Word, go to TOOLS menu, and choose Track Changes. (You should be sure the toolbar shows for this.) There are different options to show the corrections. I prefer to show them right in the document (not in balloons off the the right, or in a window at the bottom).
The best advantage of this method is that students can learn from each others mistakes. I often BOLD the common mistakes and teach a mini-lesson on that point. Timing is everything (do get the feedback in the next class, research shows it is most effective that way).