You need to do like below. you need to call the RefreshContent function on onload function.
HTML
<body onload="RefreshContent()">
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<div>
<table>
<tr>
<td>
<asp:UpdatePanel ID="Updatepanel1" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true">
<ContentTemplate>
<div>
<table>
<tr>
<td style="font-weight: 700; text-align: center">
<label id="Label2">
From</label>
</td>
<td>
<asp:TextBox ID="TxtFrm" runat="server" class="date"></asp:TextBox>
</td>
<td style="font-weight: 700; text-align: center">
<label id="Label1">
To</label>
</td>
<td>
<asp:TextBox ID="TxtTo" runat="server" class="date"></asp:TextBox>
</td>
<td>
<asp:Button ID="Button1" Text="Save" runat="server" OnClick="Save" />
</td>
</tr>
</table>
</div>
</ContentTemplate>
</asp:UpdatePanel>
</td>
</tr>
</table>
</div>
<script type="text/javascript">
$(document).ready(function () {
PopulateDatePicker();
});
function RefreshContent() {
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(PopulateDatePicker);
}
function PopulateDatePicker() {
$('#<%=TxtTo.ClientID%>').datepicker({
changeMonth: true,
changeYear: true,
yearRange: '-5:+0',
duration: 'fast',
dateFormat: 'dd-M-yy',
showAnim: 'slideDown',
maxDate: '0'
});
}
</script>
</form>
</body>
