How to display PDF file in Iframe which are in Folder by clicking Image button in MVC4

I have a folder called PDF in the application . I have stored 2 pdf files.

In the view :-

  <a href="~/UserSettings/GetSocialPDF" target="iframe_a">

          <img id="imgfinancialProcess" src="~/images/social_options.png"  height="250px" width="250px"/>

  </a>


 <a href="~/UserSettings/GetoptionPDF" target="iframe_a">

          <img id="imgfinancialProcess" src="~/images/options.png" height="250px" width="250px" />

 </a>

And i have  i frame in my VIEW. Please find below.

<iframe src="" name="iframe_a" style="height: 1000px; width: 1400px"></iframe> 


In my Controller :-

1) 
 public FileStreamResult GetSocialPDF()
        {
            FileStream fs = new FileStream(Server.MapPath(@"~\pdf\Socialsheet.pdf"), FileMode.Open, FileAccess.Read);

            return File(fs, "application/pdf");


        }

2) 
 public FileStreamResult GetoptionPDF()
        {
            FileStream fs = new FileStream(Server.MapPath(@"~\pdf\Option Appraisals Web Portal Specification.pdf"), FileMode.Open, FileAccess.Read);
            return File(fs, "application/pdf");

        }