how to download a pdf file stored in a server in client side in node.js server

how to download a pdf file stored in a server in client side in node.js
server

How to download a pdf file stored in a server in client side in node.js
server.
pleas some one help me out in this code.
fs.readFile('temp/xml/user/username.pdf',function(error,data){
if(error){
res.json({'status':'error',msg:err});
}else{
res.json({'status':'ok',msg:err,data:data});
}
});