I have Adobe RoboHelp9. How do I make it useful for editing the RoboHelp 12 projects?

Rh projects are really version specific. Once opened in the highest version, they cannot realistically be worked on in earlier versions.

There are back door ways of opening a higher version in a lower version but any code that is specific to the higher version will give problems. I believe there is up to date version on how to do that on Willam van Weelden's site at  http://wvanweelden.eu

If the topics have simple code only, you may be able to import the topic into your version, make the changes and then let your teammate import back but I wouldn't like to be doing that for any significant amount of work and you would have to check carefully each time.

The real answer is to upgrade to Rh2015.

See www.grainge.org for RoboHelp and Authoring tips

@petergrainge