$sOriginal) {
    $sKey = $aMatches[1][$i];
    if (isset($aFiles[$sKey])) {        
        $sFile = str_replace('\\', '\\\\', $aFiles[$sKey]);
        $sField = sprintf(':%s:PDF', $sFile);
        $sNew = preg_replace('~[\s]*file[\s]*=[\s]*\{[^\}]*\},?([\n\r])+~', '$1', $sOriginal);
        $aFields = explode(',', $sNew);
        $sNew = rtrim($sNew, "\n\r}");
        if (substr($sNew, -1) !== ',') {
            $sNew .= '},';
        }
        $sNew = sprintf("%s\nfile = {%s}\n}", $sNew, $sField);
        $sDatabase = str_replace($sOriginal, $sNew, $sDatabase);
    }
}
file_put_contents($sBibliography, $sDatabase);