pdf_file = models.FileField(_('PDF file'), upload_to='books/pdf', blank=True)
odt_file = models.FileField(_('ODT file'), upload_to='books/odt', blank=True)
pdf_file = models.FileField(_('PDF file'), upload_to='books/pdf', blank=True)
odt_file = models.FileField(_('ODT file'), upload_to='books/odt', blank=True)