jqdocumentextern.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>CARREGAR LA PÀGINA AMB INFO EXTERNA</title>
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.5.3/dist/css/bootstrap.min.css" integrity="sha384-TX8t27EcRE3e/ihU7zmQxVncDAy5uIKz4rEkgIXeMed4M0jlfIDPvg6uqKI2xXr2" crossorigin="anonymous">

        <!--CARREGAR FRAMEWORK DE JQUERY-->
        <script src="http://code.jquery.com/jquery-3.5.1.min.js"></script> 
    </head>
    <body>
        <input type="button" value="CARREGAR" id="btn-carrega">
        <div id="capa"></div>

        <script language="javascript">
            $(function(){
                $("#btn-carrega").click(function(){
                    $("#capa").load("extern.txt");
                });
            });
        </script> 
    </body>
</html>