To answer this question, I posted this tutorial regarding two AddOns: Workflows and Collavate. Both of these AddOns are available for Docs and Sheets and work great for document review/approval. Take at look at the tutorial and then use the links below to find these AddOns.
Workflows - https://goo.gl/MQTbdr
Collavate - https://goo.gl/yEvUlv