If they are not DRM then use the free Calibre to convert them to whatever is convenient.
You'll also probably find Calibre much better than ADE for all non-DRM book tasks (reading, transferring, managing, converting, etc)
The .epub files should be readable on ADE even if DRM; reading DRM .epub files is really what ADE is for.
I'm almost certain ADE cannot read .LIT files.
You may be able to remove DRM from .lit files using a DRM stripper such as epubee.
I do NOT advocate using such code to get around the valid limitations placed on a DRM book.
However, where the problem arises only because problems with DRM infrastructure and its implementation, such a measure is totally justifiable.
As the .lit format appears to be deprecated, that may well justify the use of such code.