Using a *simple* version control system with a *simple* graphical user interface might go a long way to convincing them to use versioning. I would suggest SVN w

Using a *simple* version control system with a *simple* graphical user interface might go a long way to convincing them to use versioning. I would suggest SVN with TortoiseSVN, and would most strongly argue against GIT. Yes, all the cool kids use GIT. For simple users, SVN is something that's easy to understand and that they cannot get wrong. They are also highly unlikely to need to rebase their .xslx files. We managed to get the sales people to use SVN for their work on proposals. Now the proposal is simply called "project name/proposal.docx", instead of having dozens of documents with unclear provenance around, possibly over multiple machines. In addition to that you can lure them in with the option to roll back to old data, and central backups.