That depends on the type of device that you are using.
If you have a Mac or Windows device - a PC or laptop, there no longer is any alternative to Adobe Digital Editions. If you have a mobile device, then the Pocketbook app - available for Android and Apple will open .acsm files (acsm is the format used for ebooks with DRM). You will still need an Adobe ID to open the acsm file in the Pocketbook app.
Installing Adobe Digital Editions tutorial (included section on creating Adobe ID)
If you can't use Adobe Digital Editions on your desktop device, perhaps it is simpler to read the book online rather than download it.
Alternatively, in addition to printing and copying ProQuest Central ebooks, you can download a limited number of pages per day. This download DOES NOT require Adobe Digital Editions and can be opened in any app that reads EPUB or PDF files. See the book homepage for printing/copying/download allowances.
