Well, you shouldn't. Proceed with programming, I mean. You haven't got your requirements clearly specified yet, so it's too early to start programming.
First you have to get your requirements clear. "Convert XML file to
Word file" itself isn't clear -- there are many ways to do that. So you need to specify what it means to you to convert an XML file to a Word file. Other people may do it differently, but that's because their requirements are different than your requirements. You need to specify what YOU want to happen.
Once you have a complete set of requirements, you won't have a problem with unexpected XML tags. That's because your requirements will cover what to do for any tag. So get started with requirements definition.