DocumentHandler::getConvertExtension

static function getConvertExtension($extension)
{
	static $convertFormat = array(
		'doc' => 'docx',
		'.doc' => '.docx',
		'xls' => 'xlsx',
		'.xls' => '.xlsx',
		'ppt' => 'pptx',
		'.ppt' => '.pptx',
	);
	if(isset($convertFormat[$extension]))
	{
		return $convertFormat[$extension];
	}
	if(isset($convertFormat[mb_strtolower($extension)]))
	{
		return $convertFormat[mb_strtolower($extension)];
	}
	return null;
}