In lighttpd, to disable PDF opening in browser, add following config files in lighttpd.conf. This is useful in increasing CTR as browsers usually get stuck while loading PDF files.

$HTTP["url"] =~ "(.*)\.pdf" {
mimetype.assign = (".pdf" =>"application/octet-stream")
setenv.add-response-header = ( "Content-Disposition" => "attachment" )
}

Dont forget to enable setenv module, if not already done …

server.modules += ( "mod_setenv" )

service lighttpd reload