Downloading Kobo ebooks onto Sony ereader

I bought books on the Rakuten Kobo website and the books are shown on the Kobo Desktop. But I can't download them onto my Sony eReader. I was told to download Adobe Digital Editions. How can I get the books from the Kobo Desktoip into the ADE program and then onto the reader?

It also seems like I can't authorize my eReader on ADE. ADE doesn't recognize it when plugged in.

I appreciate any help ad neither the Kobo help center nor the Adobe Help Centre were able to assist.