how to block right mouse click on iframe

How do I block the right mouse button click on top of the iframe, I tried to use the oncontextmenu="return false" in the iframe tag but it didn't work, in my case I want to change the right button on top of the pdf that I do this being a example inside the iframe, here is an example inside my code:

<html>
<head>
    <title>block the right mouse</title>
</head>
<body >
    <iframe oncontextmenu="return false" id="iframepdf" src="http://infolab.stanford.edu/pub/papers/google.pdf#toolbar=0" width="500px" height="600px" type="application/pdf"></iframe>
</body>

Solution

This is a complete code to disable the right click

<html>
  <head>
    <title>Disable Context Menu</title>
    <script type="text/jscript">
      function disableContextMenu()
      {
        window.frames["fraDisabled"].document.oncontextmenu = function() 
         { 
            alert("No way!"); 
            return false;
         };   
      }  
    </script>
  </head>
  <body bgcolor="#FFFFFF" onload="disableContextMenu();" oncontextmenu="return 
   false">
    <iframe id="fraDisabled" width="528" height="473" src="local_file.html" 
       onload="disableContextMenu();" onMyLoad="disableContextMenu();"> 
     </iframe>
  </body>
</html>

I Hope this is useful....