CC is prepared to accept any "book extension" recognized by calibre. Currently the extensions recognized by calibre are:
Code:
['lrf', 'rar', 'zip', 'rtf', 'lit', 'txt', 'txtz', 'text', 'htm', 'xhtm',
'html', 'htmlz', 'xhtml', 'pdf', 'pdb', 'updb', 'pdr', 'prc', 'mobi', 'azw', 'doc',
'epub', 'fb2', 'djv', 'djvu', 'lrx', 'cbr', 'cbz', 'cbc', 'oebzip',
'rb', 'imp', 'odt', 'chm', 'tpz', 'azw1', 'pml', 'pmlz', 'mbp', 'tan', 'snb',
'xps', 'oxps', 'azw4', 'book', 'zbf', 'pobi', 'docx', 'docm', 'md',
'textile', 'markdown', 'ibook', 'ibooks', 'iba', 'azw3', 'ps', 'kepub']
I am not prepared to add one-off extensions to accommodate files that calibre itself will not recognize as a book format. We did that once for mp3 files (audio books) and have paid and paid and paid for that decision. I don't even know whether it still works.