The books purchased from Kobo Store should appear in your Library, if you have signed in to your device with your existing Kobo account. Your device can open only EPUB, EPUB3, PDF, MOBI, JPEG, GIF, PNG, BMP, TIFF, TXT, HTML, RTF, CBZ, and CBR
files. DRM is a technology and not a file format. A DRM (Digital Restrictions Management) file is used to protect the rights of authors and publishers. In order to fix your problems, I recommend that you contact Kobo using Contact Customer Care link from the official web page.