There's a post on the old forums that should have been imported - but the PDF it linked to has disappeared... grrrr. You could try here http://********************/tips/new-year-new-features, or List of new features
If you want to export to DBF you're probably safe going back a long way - as that format hasn't changed in a decade or more. v6 is probably fine.
If you want to read from PDFs then yes, you need v8 Pro or above, but v12 is seriously way better than earlier versions at handling PDFs - http://www.datawatch.com/video/datawatch-modeler-and-pdf-files-unlocking-the-value-from-data/.
Managing the software isn't just about the license cost - there's no point buying a nice car for a teenager who's just passed their driving test, after all - or just about putting the software on desktops and leaving the users to it - if we all spent all day driving ourselves from A to B, we'd never get any real work done. So if you're thinking about deploying Monarch/Modeler, it's not just about matching the version to the formats you need to handle, it's also about making sure the users have the right skills, and that you automate the work that ought to be automated.
If you'd like some expert help from people who've done it before, for real, please do get in touch.
All the best,