You need official, high-resolution, searchable e-books; you want to support authors; you require a commercial license for the content; or you cannot tolerate the risk of a bad scan.
EurekaDDL is a useful but ethically murky tool. Think of it as the "flea market" of academic PDFs. For a struggling student who needs any copy of a required reading, it’s a 4-star service. For a university or a professional, it’s a 1-star legal risk. Use with eyes wide open. eurekaddl