Rendering web controls as plain text into a string

Question 1

When markup is not needed then PlaceHolder and Literal are your friends :)

 <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="RenderControl.aspx.cs" Inherits="AccessibleMenu.RenderControl" Trace="true" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:PlaceHolder ID="PlaceHolder1" runat="server">
            <asp:Literal ID="Literal1" runat="server" Text="Literal1"></asp:Literal>
        </asp:PlaceHolder>
    </div>
    </form>
</body>
</html>
<script type="text/C#" runat="server">
    protected void Page_Load(object sender, EventArgs e)
    {
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        System.IO.StringWriter sw = new System.IO.StringWriter(sb);
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        PlaceHolder1.RenderControl(htw);
        Trace.Write(sb.ToString());
    }
</script>

Question 2

You have to change your HTML to use literal :

<body>
    <form id="form1" runat="server">
         <asp:Literal   ID="HelloWorld" runat="server"></asp:Literal>
    </form>
</body>

Your C# :

protected void Page_Load(object sender, EventArgs e)
{
  HelloWorld.Text = 'Your text without HTML':
}