Adobe Digital Rights Management (DRM) ensures that the person who downloads an eBook is its sole owner and is unable to share the file with others. The DRM specification for each eBook is set by the publisher who owns the respective copyrights.
Is this optional?
No. You must have a valid Adobe Id. The option on the authorization pop up which says "I want to authorize my computer without an ID" will not work. You will corrupt the download and the book will have to be re-purchased.
Where do I get an Adobe ID
You can create an Adobe ID on www.adobe.com. Your email address and a password, entered for this Adobe ID, will be the link to your Adobe ID for any software. The sign-up pages look like the images below, per March 2016.
Dutch: Inschrijf Formulier
English: Sign Up Form
You can change the language/region in the footer on adobe.com if necessary, and return to the sign up page.
Step 2. Install & Authorize your Software
We advise the Adobe Digital Editions software, but there are other options. Note that you will always need an Adobe ID, regardless of the software. You must also authorize that software.
Once you've completed step 2, you can click on the download link in the email sent to you by ABC. The ADE software will automatically download the book onto your computer and you will be able to read it.