I once managed an Indie Writer contest.
The technical side, including building the website, and we listed instructions for getting Word (.doc, .docx) into a suitable format. We were inundated with questions about OpenOffice, LibreOffice, and a couple of less popular ones.
As it happened our "suitable format" was .odt, so it was simple to sort, but around 3/4 of submissions before we added an extra page for those instructions asked about it.