Refer the below sample code for your reference and implement it as per your code logic.
HTML
Parent.aspx
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<style type="text/css">
html, body
{
margin: 0;
padding: 0;
height: 100%;
}
.modalBackground
{
background-color: Black;
filter: alpha(opacity=40);
opacity: 0.4;
}
.modalPopup
{
background-color: #FFFFFF;
width: 80%;
border: 3px solid #0DA9D0;
}
.modalPopup .header
{
background-color: #2FBDF1;
height: 80%;
color: White;
line-height: 30px;
text-align: center;
font-weight: bold;
}
.modalPopup .body
{
min-height: 50px;
line-height: 30px;
text-align: center;
padding: 5px;
height: 80%;
}
.modalPopup .footer
{
padding: 3px;
}
.modalPopup .button
{
height: 23px;
color: White;
line-height: 23px;
text-align: center;
font-weight: bold;
cursor: pointer;
background-color: #9F9F9F;
border: 1px solid #5C5C5C;
}
.modalPopup td
{
text-align: left;
}
</style>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script type="text/javascript">
function ShowModalPopup() {
$find("mpe").show();
return false;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</cc1:ToolkitScriptManager>
<div>
<br />
<br />
<asp:Button ID="btnShow" runat="server" OnClientClick="return ShowModalPopup()"
Text="Show New Page" />
<asp:LinkButton ID="lnkFake" runat="server"></asp:LinkButton>
<cc1:ModalPopupExtender ID="mpShow" BehaviorID="mpe" runat="server" PopupControlID="pnlPopUp"
TargetControlID="lnkFake" BackgroundCssClass="modalBackground" CancelControlID="btnClose">
</cc1:ModalPopupExtender>
<asp:Panel ID="pnlPopUp" runat="server" CssClass="modalPopup" Style="display: none">
<div class="header">
New page in iFrame
</div>
<div class="body">
<iframe id="iFramePersonal" src="142112_ChildPage.aspx" height="100%" width="100%">
</iframe>
<br />
<br />
<asp:Button ID="btnClose" runat="server" Text="Close" />
</div>
</asp:Panel>
</div>
</form>
</body>
</html>
View.aspx
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
This is New page in Modal Popup
</div>
</form>
</body>
</html>
Screenshot
