Why do I need to activate my computer with my Adobe ID?
Some digital publications that you purchase online or check out from a library may contain digital rights management (DRM) protection that restricts the items from being shared with others. Digital Editions helps ensure that your eBooks and other digital publications are not "locked" on one computer. They are assigned to you through an ID, and can be viewed on any compatible device you own that you activate with that ID.
and this one:
Can I transfer eBooks that I have already purchased or downloaded to another computer?
1. If you activate your computer with Digital Editions anonymously, all the purchased or borrowed books afterwards belong to that computer. [!!!!]
2. If you activate your computer with Digital Editions with an ID, all the purchased or borrowed books afterwards belong to that ID.
3. The books downloaded before activation will not be converted.
4. Books can be copied from one device to another device. If two devices are activated with the same ID, purchased books can be opened on the other device.
[!!!!] If the other device is not activated or if it is activated with another ID, a pop up window will appear to ask for ID when opening the purchased books. Borrowed books cannot be opened on another computer regardless its activation status. It is because that the loan token is not copied.
5. Borrowed books and their loan tokens will be copied when transfer(ing) (not copy [!!!!], this is an ADE feature) them between computer and device (e-reader).
6. If the permission limits the books to be viewed on only one device, the copied books will not be able to be opened.