Here's a fork of your Plunker: http://plnkr.co/edit/xyPqyl20C4sVL11KqNCS?p=preview
What was changed:
The navigation buttons (forward and back) were given an unique class navigate
<a href="#" class="navigate" id="back">back</a>
<a href="#" class="navigate" id="forw">forward</a>
The href attributes were changed to represent the next and previous pages (id_1, id_2, id_X, ...)
Because the navigation links change with the page, an onclick listener was added to the document.
//Listen to all clicks
document.onclick = function(event) {
    var el = event.target;
    //If we clicked a navigation link
    if (el.className == "navigate" && el.nodeName == "A") {
        //Change the page
        move(el);
    }
};
(Source: Click event on dynamic element WITHOUT jQuery )
Created function move() to change between pages.
  function move(el)
  {
    if (el.getAttribute("href"))
    {
      //Get hash without #
      var hash = el.getAttribute("href").split("#")[1];
      //Change content based on hash
      document.getElementById("putIn").innerHTML = document.getElementById(hash).innerHTML;
    }
  }
A better solution would be to move the navigation links outside the #putIn div and just keep track of what "page" is currently displayed. This would enable you to add / remove pages without the need to update the code.