Open a file on the server and then save it

this is my problem:
I have a link to Open a file (I  have found this way cause with a simple link it would have been marked "readonly")
<a href="../DownloadFile.aspx?file=test.xls"> Open file </a>

 
The code in the .aspx page permit to download the file with the header 
Response.AddHeader("Content-Disposition", "attachment; filename=" & file.Name)
 
So when the user click the link he is prompted wiht a Message box sayi ...