Downloading PDFs from website

My calculus class uploads the book onto a website so we don't have to purchase it. Once logged in, I can access the book which is divided by class level (I,II,III) and is in PDF format. How can I mass download this book without having to go through each section and downloading each individual chapter(that's how they're seperated)

wget -r -np --http-user=USER --http-passwd=PASS http://whatever/

curl -O http://domain/file{I,II,III}.pdf