Force download box does not appear

Hi,
I’m trying to force the ‘download dialog box’ to appear once the page is loaded with a given filename in the url. However, the file (in this case a pdf file) keeps opening in the browser and showing all funny codes. I’ve tried with all sorts of header combinations from different tutorials, but it never pops up in either Firefox or IE. Any ideas?
Here is my code:

[CODE]if(file_exists($folder.$file)) {
header(“Pragma: no-cache”);
header(“Expires: 0”);
header(“Cache-Control: must-revalidate, post-check=0, pre-check=0”);
header(“Content-Type: application/force-download”);
header(“Content-Length: “.filesize($folder . $file));
header(‘Content-Disposition: attachment; filename=”‘.$file.'”‘);
readfile($folder.$file);
die();
}[/CODE]

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