The only ways to share a prototype would be the HTML export or adding them as a Reviewer for review mode.
Anyone who has access review mode as the ability to add discussion topics (or reply to one), but they are unable to make any actual editing changes. You would need to notify these users to not comment. One thing you can do is duplicate the project and only allow those users to view the copy. That way you can have one project that is clean and the other with everyone's thoughts.
Otherwise, you can always publish the HTML export online. Publishing an export will give you a link that you can pass around to easily view the prototype from any computer. It saves you the trouble of dealing with files and there is no review mode.