Mime type extended, for upload files in WordPress

functions.php

add_filter('upload_mimes', 'custom_upload_mimes');
function custom_upload_mimes ( $existing_mimes=array() ) {
    // add the file extension to the array
    $existing_mimes['cdr'] = 'mime/type';
        // call the modified list of extensions
    return $existing_mimes;
}