Books that are not in the public domain are the intellectual property of the author of the book (or to whomever has received rights from the author). DRM technologies are used to limit the amount and type of access and control a consumer has over the book after purchasing it. For instance distributors of information may limit the number of pages that can be downloaded at any one time, limit the ability of the consumer to share the book, or make the book 'vanish' once a loan period is completed.
Of the e-book vendors at Penn, Ebscohost and Proquest platforms are the most likely to have DRM restrictions on their books. Usually there is a 50 page restriction on downloading but you can go back the book on a different day to download additional pages or chapters. Often you can download chapter by chapter (again, likely not all in one visit).
If you are downloading an entire book, you'll need to set up your own account within Ebscohost or Proquest and then follow the instructions. Downloads for ebooks with restricted access are not permanent.
