Yes, approvers can edit documents that require their approval, so long as those users have been granted the access permission to edit those documents.
In addition, approvers can approve or reject the document or transaction that was sent to them. If an approver chooses to reject the transaction, they can leave a note about why the transaction or document is being rejected.
The rejection notification will be sent to the user that initiated the transaction. The initiating user may then make edits to their own document or transaction, which will reset the approval requirements for their action.