If you do your own ebook formatting and don’t use a program like Vellum or Jutoh, there’s a good chance, especially if you’re enrolled in Kindle Unlimited, that you provide a word document to Amazon and let it convert the book into its format. Then, you download the finished file from their site to share with your review team.
In a way there’s nothing wrong with that. However, it also limits your options. Not every reader or reviewer uses a Kindle, and I’m hearing that when you download the book from Amazon it’s already applied it’s DRM, meaning that the file often can’t be transferred to another device. (This hasn’t been confirmed, but I’m hearing it.) So let’s look at the various formats and what you might need.
PDF Files are still often used by reviewers, especially for nonfiction as well as children’s books. They can be emailed to a Kindle to covert them into a Kindle document and can be used on the widest variety of devices. However, they are also considered among the easiest to pirate. Personally, I don’t provide PDF files when submitting my books to reviewers.
Epub Files are used by most non-Kindle reading apps and you can upload them to Smashwords. Scrivener can compile books directly into epub files and you can upload them to Amazon. If you’re uploading ARC files to a review service, I’d include an epub file because you never know what your readers might want or need.
Mobi Files are read by Kindles and Kindle app. These files can be emailed to your Kindle, transferred with a USB cord, and are Kindle native, so they’ll read in the docs or in the books folder.
A good formatter will make sure you have all three formats, if desired, and will be well versed in keeping the file size down, especially since bloated files will cost you money.