If your question is, "is proofreading included in my conversion," the answer is no.
Naturally, we look over each book, and try to ensure that it's reasonably error-free before we send it to you for review; but as the publisher, you are responsible for proofreading your own book, both before and after conversion, just as all publishers are. We convert manuscripts/books from your format or file into eBook format, just like a printer would do. Whatever goes in for conversion, comes out after conversion. Make sure, when you're reviewing your book for conversion, that you review our policy for copyedits post-production.
We of course will correct any error made during the conversion process at no cost to you.
Will you provide proofreading if asked?
If you want to arrange for a proofreader during conversion, we're delighted to recommend someone to you. Simply contact us (and feel free to do this at any time, whether you're a client or not!) for the name of some first-class proofreaders, or check out our FAQ article for our recommended editors: Recommended Editors.