As part of the new Google Drive, we are updating Drive’s viewer. The new viewer is faster, cleaner and provides easier ways to connect with third-party Drive apps. It also brings a unified viewing experience across Drive content and Gmail attachments. Note that as part of this change we will remove support for adding file-level commenting of non-Google file formats. This change doesn’t impact comments in Google Docs, Sheets and Slides, and existing comments on non-Google formats will be retained and available to view.
Rapid release and Scheduled release (rolling out gradually)
For more information:
Reference by: www.google.com