Another possible way is to install the Sony Reader software
https://ebookstore.sony.com/download/
That is designed to be used with Sony eReader devices, but I think it will work fine anyway.
Not a particularly good bit of software, but I seem to remember hearing of a case where ADE always hung in the process of downloading a .epub file from a .acsm but the Sony reader would succeed in the same task.
Try: if it works you should be able to get it onto the Kobo.