如何创建下载链接来下载文件而不是重定向到浏览器?

I am trying to put a link to download a pdf from server, instead of redirecting the browser to open the pdf in another page. I have seen such options in many sites but unable to get the code. And most people says it should be possible with php only, could anyone help me for this.I am trying to put a link to download a pdf fro