Kobo sells their books in two formats. One is their own "Kobo ePub" that you can view on their devices, apps and the desktop application. These can't be viewed in any other way.
The other format is the usual epub. These can be downloaded by clicking the "Adobe ePub" link in your library on the Kobo shop site. Most will have DRM and are downloaded via ADE and you can read them there. Any without DRM will download directly and can be added to calibre.
I think you will find the ePub version will be more practical for what you are doing.