Can a reviewer attach a file to the Approval Module?

The reviewer cannot attach a file to the Approval Module

What the Reviewer can do is copy the link of a file in Drive to the Approval module Comments section. 

The next Step Reviewer will receive the link to the file in the Request for approval email they receive. Ensure you have given the correct sharing permissions in your Drive.

The Requester will also receive the link from the Reviewer if you have set-up Send back to Requester.