Smashwords ought to have an option to let you upload an epub. Alas, they don't; they insist on getting a doc file that is run through their "meat grinder" to create many forms of files, including mobi and epub. In theory, it's brilliant. In practice, you will be happy to sell them your mother for an easier way to get your books to Apple, Sony, Kobo, and the other sites that Smashwords serves.
Mind you, I do sympathize with Smashwords, and I think they provide a great service for a very fair cut of the action.
But their meat grinder can grind and grind before you'll get a decent result. When you succeed in getting one file through satisfactorily, you may get smug and think you've mastered the meat grinder.
But you are the meat grinder's bitch. It will laugh at your next efforts and dare you to try again.
The problem is that the meat grinder is very finicky about what it'll process. Doc files can retain all kinds of invisible code that won't show up when you choose "show invisibles" because they're just that evil.
Smashwords' recommendation in these cases is to save your file as text in order to eliminate all code. Including your carefully chosen italics and bolds. And then you start all over again, reformatting everything.
Fortunately, there is a better solution. Stay tuned for my next post on epubbing.