Have you come across our Community Extensions product? It's a companion to Document! X and HelpStudio that allows you and your users (or reviewers) to add private notes, public comments and ratings against topics in the help systems you create. As well as the functionality in the output you create...

Community Extensions is ideally suited to this. Users / business stakeholders can record comments and feedback from directly within the generated help system and you as the author can easily review a list of comments using Tools\Community Content within HelpStudio. You can find more info about Community...