When you download ADE to a computer, you authorize it for that computer through an Adobe ID that is connected to your account. If you use a device that has someone else's Adobe user ID assigned to it, you may de-authorize them and re-authorize yourself using your credentials. A maximum of 6 devices may be synced to an Adobe ID.
When ADE is first downloaded, it is authorized to the user that downloaded it.
With Adobe Digital Editions open, you can de-authorize the previous user and then re-authorize to your account. Use the Command CTRL-SHIFT-D while in ADE to de-authorize a user.
When you click the Library dropdown in ADE and select "Authorize user"
Then you can authorize that copy as a different user.
If you connect to a device that is authorized with a different Adobe user ID, it will not recognize your device until you de-authorize and reauthorize with your Adobe ID. To recap, eReader devices are tied to an authorization once it is used with ADE. The device using ADE will recognize all materials authorized with that Adobe user ID.
If you cannot get a copy of ADE to recognize your device:
