There are a number of technologies for giving feedback on a document. Inline annotation/markup of the document is a common way to provide specific feedback on particular words/sentences/sections of a document. If a document is uploaded to a site that has supports discussion or forums, then feedback can be provided via those features. Finally, feedback can also be given via email.
How to do it:
To give feedback on a document via Inline comments, see: Annotate/Mark up a Document.
Online Discussion Feedback
To give feedback on a document via online discussion, the document owner should be asked to upload the document to a site that supports online discussion such as a blog. Once the document is uploaded, then blog visitors can view the blog post that includes the document, download it and then comment on it via the comment link that is included in the blog post.
Email can be used to send a document for feedback, as well as send back feedback on the document via the email text or through the inclusion of a copy of the document with inline annotations
Google Docs Feedback
Google Docs allows a document owner to share their document with others who can then insert comments. Unlike Microsoft Word, which requires commenters to add comments to their own copy of the document and then send their copy to the author, Google Docs allows the author and commenters to share the same document.