Do you have Microsoft Office files in your Google Drive account? When you click on them to open, it always opens as a preview. Did you ever wonder if you could do anything else with this preview? Well, you can!
Of course, you can print and download the file, but if you are collaborating with other people, you can also comment on the file.
Highlight what text you want to comment on, and then the comment icon will appear off to the side. Comment on the file just like you would do in an actual Google file.