With the Advance Reading Copies you'll download from Booksprout, you'll often have the choice of three different formats depending on which ones have been supplied by the author.
MOBI - EPUB - PDF
When you choose direct download on the ARC page, you'll be shown the file types available for that ARC, such as in the image below.
Choose MOBI if you have an Amazon Kindle or will be reading on the Kindle app downloaded for your computer or laptop.
Choose EPUB for most other eReaders including the Nook.
Choose PDF if you prefer reading on a laptop or desktop computer. You'll need Adobe Reader or a compatible program in order to read a PDF file.
Do you have a device not mentioned here or further questions? Contact support.