Advice about eBook Readers for Mac/PC Forgive me for my ignorance but, I recently purchased an eBook only to find that I also had to download Adobe Digital Editions in order to be able to view it on my Mac.  The PDF that I downloaded in the process is encrypted.  Does this mean that I can only view it using Adobe Digital Editions, or can any ePub Reader (including any that I install under Windows) be able to read it?

I know that there are many (better) ePub readers out there, the prominent ones of which are listed in the following post.

What could I use to read epub books on OS X?

If I now were to install Calibre, for example, would it interfere with Adobe Digital Editions?

Note that I bought the eBook from http://www.ebook.com.  This is the message I get when I try to double click on the PDF file to open it using Acrobat Reader:

This document requires digital rights management (DRM) features supported
by Adobe Digital Editions. Would you like to open it in Digital Editions now?


This is the information that I have been able to retrieve about the file using Adobe Digital Editions:

Permissions set by the publisher
  Allow viewing: on any device
  Allow copying: 5 copies with an additional copy accrued every 6 days,
  capped at 5 copies, on any device
  Allow printing: 20 pages with an additional page accrued every 1 day
  12 hours, capped at 20 pages, on any device
ePub is a digital publishing format, but it's not as straightforward as you might hope, in that not all ePub files are the same.  There are 3 main types of ePub in the wild today:


Straight ePub, any ePub reader should be able to open these
ePub with Digital Rights Management protection:

Adobe Digital Editions
Apple iBooks from the iBooks store



The protection mechanisms are portable to an extent, you can see the Digital Editions protection on other formats other than ePub.  The main takeaway is that to read the file, you need a compatible reader.  For the non-protected files, that is straightforward enough.  Pretty much anything can read them.  For the protected ones, it's more difficuly.  Adobe protection is compatible with a small number of desktop apps for a bit of extra portability, but iBooks ones can only be opened in iBooks in iOS, full stop.

It's a pain, and like the MP3 fuss we are starting to see people dropping DRM entirely from their ebooks.