The wider implications of recommending a proprietary application (worse: a GUI based one which costs money and is only available on one platform) is that now your documents are tied to a particular time of reference in an ecosystem. Something which moves.
I am not an OmniFocus user, recent versions of OmniFocus can export data to the TaskPaper format (which is just plain text) or to a CSV file.
I am not an OmniFocus user, recent versions of OmniFocus can export data to the TaskPaper format (which is just plain text) or to a CSV file.