In addition to being able to view other document types, users can now take action on Office, PDF, or image files as if they were native Google Drive formats. In the Drive preview pane, comment, assign tasks, or mention coworkers and the people you work can reply back, even if they're not using G Suite. read more
Yes and no. You can comment on the contents of a PDF file but you have to convert it to Google Docs format first. After you have uploaded your PDF document to Drive, right click on it and select Open with > Google Docs. read more