Problem forcing a download

Hi, I am trying to force licks to files to open a file save dialog box, whatever the file type is. I have the following link on my page (the page links back to itself): <p>Click <a href="view_document.php?file_name='.$file_name.'&view_document=true">here</a > to download the document</p>'; I also include a file at the top of each page (top.php) for function calls and in this file I have the following: //view document if(isset($_GET[view_document]) == true){ Header('Content-Type: application/octet-stream'); Header('Content-disposition: attachment; filename='.$_GET[file_name]); } when I click on the link I get the dialog box popping up but it downloads the code for view_document.php. I am obviously doing something silly here but I can't work it out, I would be very grateful for you advice here.