Doitsu is correct that our Smashwords Direct feature only accepts epubs at this time. If you want to have other formats in addition, you should upload a word document in addition to your ePub. Depending on what you are using to create your ePub, if you start with html, you may be able to convert a reasonable clean word document from the ePub document. (
Pandoc can convert form html to docx if you need it.)
Most of the people who have trouble with their Word document uploads don't actually know how to use Word styles, which is important to keep the document clean for the conversion *to* ePub. If you're coming *from* a reasonable clean conversion engine, you should be fine.