What versions are involved? You'll have to export to Interchange format,but whethr you can do it only once, or if yo have to open and re-xport in all intervening versions depends on waht both of you are using.
This is not a great workflow for collaboration, expecially if you use any advanced features in your version that are not supported in theirs. Those will be lost entirely. There is a significant risk of text reflowing and changing line endings, too.