Digital editions3

I Have ipad air and kobo mini ,no other computer. I downloaded digital editions but it went into BT cloud ,they say I cannot open these files as there is no app for them. I didn't have any options as to where the download went, can anyone tell me how to move the files , I can't get any answers from bt. I am complete novice on computers ,I got the ipad as I am deaf so this is the only way I can communicate. Hope someone can help please.