DRM protection on my epub files

Hello everyone,
I bought several eBooks in epub format over the years, I read them on my Kob eBook reader, which just recently broke down permanently. While waiting to be able to buy a new one, I installed on my Android smartphone a specific application for reading epub eBooks. I tried to move a file from my "Adobe Digital Edition" library, to try to read it on my smartphone, but I get a warning that the file is protected and I cannot read it. Being the owner of the file, purchased regularly, how can I overcome the problem, always in an absolutely legal way?
Thanks any contribution will be appreciated.
regards

Ignazio