Thank you for this important question. 
First for those of you who asking why this is important, then I wish to recall what we do today when we are using Office tools. 
When we use Office tools such as Work in specific we usually turn the document around people to comment and review in track changes those changes in the document. If we look at the practical part of this process we can end up with a final document that contains many changes that hard to track.
The questions is how we do it in QPack since QPack is not an Office tool but yet when we write documents in QPack we do build the whole structure in QPack as it was document. There are paragraphs and requirements all over it.
So we can talk about two feature that together are used in order to be able to review changes on document after it has been released for review.

• Create Tag
• History Log
• Share Item

Before I start there is one behavior I need to describe in QPack that make all this happens. It is related to how QPack trace changes in child items of a DOC work item. The idea is behind the face that every change that we do to a child item of a DOC work item shall be logged in the history of the DOC work item. Why? because the regulation requires from us to create a change log history in our document and we do it today building manual table of change log history. So in QPack we built that capability automatically, and change log history can not be pooled automatically from the system.
So if you wish to start a review process on a DOC work item first you need to create TAG, what it s a TAG and I how do I activate it?
A TAG term was taken from the world of source control and the same as we preserve points of changes in the source control we do the same here in QPack. A TAG will make a DEEP copy of work item to include all the work item meta data such as Attachment, Discussion, History etc. 
How to Activate the TAG option?
To active the TAG option on your account in QPack we need to grant that permission in the QPack Admin, on the user group permission sets.
How To Create A TAG?
To create a TAG you will need to select the DOC work item you are about to release for review and right click on that DOC item to Create Tag. The creation of a Tag will prompt you to give a name to the Tag. The system shall select a default name for you but this time you wish to give your own name. For example Tag_First_Review_Before_CDR this tag name will be showing on the DOC item and all its child items if  you look at the history. Now the system “Colored” all the items with the same Tag and that Tag can be retrieved back at any time.
How Do I perform change on reviewed document?
Now that the document have been tagged you can use the Share feature to share the DOC item with your colleges for review. The share will send an email notification with link to your document for users to view and review the document. Any change made on the document by the review group will be logged on both  on the history of the item being changed as well on the history of the Parent DOC item.
How Do I Review Changes Since the Last Tag point?
Going now to the history tab of the DOC item you will find that all the changes made by all the reviewers in the document content (child Items) were logged in the history of the DOC item, and those changes that involved changes in description in specific were flagged by the system with DIFF button to allow you to see the changes in particular in diff mode.