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. 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 copy-edits post-production.
We of course will correct any error that we 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.