I accidentally bought a book with Adobe DRM on it at bol.com. When I downloaded the book I didn't get an epub but a file ending in .acsm.
Going back to the site, they claimed that I had to (1) sign up at Adobe for a ID, (2) install a Windows installer on my Linux box (?), and (3) use that software to move the drm'ed book to my sony reader. Which made me very cranky.
Fortunately, (2) and (3) turned out to be false claims, while (1) was not really necessary. On my reader (Sony PRS-T2) I simply had to choose More Content which presented me with a form to let Sony create an Adobe ID for me, or insert the ID which I just got form the Adobe site itself. Then I needed to log in at Adobe, after which something happened that I don't understand yet, but I can't claim is user unfriendly: having logged in at Adobe I was redirected immediately to my bol.com account to log in there, and I was presented with a bookshelf containing my bol.com books, including the one I just bought. Clicking that I'm guessing it was downloaded in some form, at least it became available for reading.
According the the wikipedia page of today, this should not be possible:
Compatibility with Adobe digital rights management (DRM) protected PDF and ePub files allows Sony Reader owners to borrow ebooks from lending libraries in many countries.
The DRM rules of the Reader allow any purchased e-book to be read on up to six devices, at least one of which must be a personal computer running Windows or Mac OS X. Although the owner cannot share purchased eBooks on others' devices and accounts, the ability to register five Readers to a single account and share books accordingly is a possible workaround.
To be clear, at least the PRS-T2 seems to be able to cope with Adobe's DRM without external windows or mac software, but it may depend on your location¹, and where you bought your digital book.
By the way, .acsm stands for Adobe Content Server Manager. A file with that extension contains a key or license to download a digital book. I'm guessing that the book is somehow securely saved on the reader, somewhere where the user can't access it directly.
As far as I can tell so far, the Adobe ID is needed to validate a device (your reader) as a platform to read the digital books. Maybe this means that after you've validated your device, you can also put .acsm files directly in the [media]/READER/Sony_Reader/Digital Editions/ folder, but I haven't been able to check that.
