After purchasing a DRM-protected ebook based on the .acsm/.epub format protected by Adobe Digital Editions, you may want to read the ebook on a operating system (e.g. Linux), device (e.g. Laptop), or in a format (e.g. PDF), which is not supported by Adobe Digital Editions. The following tutorials shows how read such ebooks on not supported platforms.

Please note that the following steps may only be legal in your country on your own platforms for ebooks for which you have purchased a license. DRM-protected E-books without DRM-protection may not be distributed.

The basic idea is

1. to import the DRM protected ebook (.epub) using the Adobe message file (.acsm) on a supported platform (e.g. Windows 10, Android) using Adobe Digital Editions Reader.
   Note: On MS Windows the .epub files are stored in th path “%Root%\Users\(user name)\My Documents\My Digital Editions\”; On Android “{Main Storage}//Digital Editions/”
2. to export the encryption key of Adobe DE on a supported platform (e.g. Windows 10)  from the Calibre program (+ DeDRM plugin) WITH an installation of Adobe Digital Editions
3. to import the encryption key of Adobe DE on an unsupported platform (e.g. Linux) to the  Calibre program (+ DeDRM plugin) WITHOUT an installation of Adobe Digital Editions.
4. to import the DRM protected ebook (.epub) on the unsupported platform (e.g. Linux)

Once Calibre has imported the encryption key (default_key.der) one can read DRM protected ebooks and convert them to other unprotected formats without the steps described below, ie one has to go through this tutorial only once.

A) To Do on a platform SUPPORTED by Adobe Digital Editions (e.g. Windows 10):

1. Install Adobe Digital Edition [Link]
   Note: Adobe Digital Editions is a program used to manage and read eBooks as well as other digital publications
2. Download .acsm file from your bookshop
   Note: An ACSM file is a message file served by the Adobe Content Server to Adobe Digital Editions. It contains data used to activate and download an eBook. It does not contain the eBook itself.
3. Retrieve DRM-protected epub file using Adobe Digital Editions
   Note: You have to go to the default folder where Adobe Digital Editions stores its files. 
4. Install Calibre [Link]
   Note: Calibre is a cross-platform open-source suite of e-book software.
5. Install DeDRM plugin for Calibre [Link]
   Note: For installation see  tutorial [Link]
6. Go to DeDRM plugin in Calibre
   1. Choose Adobe Digital Editions
   2. Choose “default_key” (encryption key)
   3. Export to file (default_key.der) file

B) To Do on a platform UNSUPPORTED by Adobe Digital Editions (e.g. Linux):

1. Copy DRM-protected epub file to the unsupported platform
2. Install Calibre [Link]
   Note: Calibre is a cross-platform open-source suite of e-book software.
3. Install DeDRM plugin for Calibre [Link]
   Note: For installation see  tutorial [Link]
4. Go to DeDRM plugin in Calibre
   1. Choose Adobe Digital Editions
   2. Import “default_key” (encryption key)
5. Add DRM-protected epub as book in Calibre
6. Open containing folder
7. Open DRM-protected epub as book

Mission accomplished!