Sometimes a "file association" error occurs on your computer, which prevents Adobe Digital Editions (ADE) from opening downloaded eBooks.
The file type that you're seeing is correct, since it's a Protected PDF that you're downloading. The program you'll need to open and read the file is Adobe Digital.
One eBook reader for all your Adobe DRM protected books across your Android Devices, iPad, Mac or PC. Adobe Digital Editions (ADE) is free-to-download and. How To Download and Install EPUB/EBOOK/KINDLE BOOK Reader For Mac or Windows PC