The short answer is possibly.
If your book is set up, and everything is perfect, and you’re using the right template, yes you can. But if there are any errors at all, that can really impede a reader’s experience. But it is, of course all down to the choices of the author.
Free conversions can happen at Smashwords (each platform only), KDP (Amazon only), though both are also OK for distributing to others, and D2D which is free of upload limitations. Do read the conversion terms though.
Of course, if you can code, Sigil lets you code content to match the site you need to load epubs to. It is epub only. Or if you are Mac, Vellum is a great option.
Kai Wilson-Viola writes under various names, and in all genres. Co-founder and webmistress of the IAG site, she writes content on request of members.
She has written several books including the Ten Hour Marketing Plan and 12×12 – tutorials for social media.
When not writing, she can be found maintaining sites, designing themes, managing a charity called the Less than Three foundation, gaming, knitting or reading.