Approver RoleThe Approver role differs from the Reviewer role in that the Reviewer is only able to comment on the item, and the Approver not only works as a reviewer but can also approve or mark an item as needing more work. An Approver also has a final say on the item status by approving the review or requesting a new one. The Approver has the option to delegate the review to other people, and can add other Reviewers to the review.
Reviewer options during the review:

Note the "Give Feedback" button on the left.
Approver options during the review (approved/needs more work):

Note the "Approval" button toggled on the top of the image and the "Needs More Work" Button toggled on the bottom.
The approver has more options available in the Tools menu than the Reviewer does. They can add more Reviewers or Delegate their approval:

Approver option at the end of a review:

Note the Mark # unmarked items "Approved" as this is a really useful option for reviews with a high number of items.
It is also important to understand that the Approval from an Approver is valid only from one Revision to the next as long as the item remains unchanged.
Approver Digital Signatures
If needed by your review protocol, you can require that the Approver reviews are digitally signed. To do this, you just need to activate the "Require electronic signatures from approvers" option during the review creation.

Finalizing Reviews
When an Approver finalizes a review, there are two options: a new revision can be requested or the review can be approved and signed.

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