Problem opening downloaded book

I purchased a book from Google Play. Downloaded it onto my desktop as a locked epub file.

Came to open it and had to do so via Adobe Digital Editions.

It asked for vendor's name, Google. My ID with vendor, my name. Password with vendor.

Rejected.

So registered with Adobe Digital Editions and used that ID and password.

Still rejected.

How do I open this file so I can load it on to my 2 Ereaders.

Thanks, Mike