note 8281 added to header

I'm coding a script which is used to download file from my server, but I want to know the mime type of the file. Because I send first the header("content-type : ") and the data. If I specify a unknown content-type, the browser will force the download, but I want the browser to recocgnize the downloaded file (as a msword or pdf file opened with the appropriate plugins). I hope that someone may help me. Thanks. http://www.php.net/manual/function.header.php