How to enable restricted dates using Jquery date picker ?

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jQuery

here i have two dates , reference date and purchase date...

1. reference date shows in label.
2.purchase date has date picker

here i want to enable 15days, from reference date to purchase date,and other dates are disable.. piz help me..
ref date dont have datepicker..

here i used jquery

<script type="text/javascript">
$(document).ready(function () {
//  var objDate = new Date("<%=Label1%>");
//var objDate = $("#Label1").val();
   //var objDate =  $('#<%=Label1.ClientID %>').val();

var objDate = $("#lbl_ref_date").val();
   var Presentyear = objDate.getFullYear();
        $("#txt_pur_date").datepicker({

      changeMonth: true,
      changeYear: true,
       dateFormat: "dd-mm-yy",
      maxDate: '+14d',
      minDate: '0d'
        });
        });
   </script>