$fileName = "text.pdf";
$file = fopen ($fileName, "r" );
//输入文件标签
Header ("Content-type: application/octet-stream");
Header ("Accept-Ranges: bytes");
Header ("Accept-Length: " . filesize ($fileName));
Header ("Content-Disposition: attachment; filename=" . time() . ".pdf");
//输出文件内容
//读取文件内容并直接输出到浏览器
echo fread ($file, filesize ($fileName));
fclose ($file);