<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<title>Primo Dialog</title>
<input type="text" id="First_Name"><br>
<input type="text" id="Last_Name"><br>
<input type="text" id="Age"><br>
<button onclick="SubmitValues()">Отправить</button>
<script type="text/javascript">
var First_Name = document.getElementById("First_Name").value;
var Last_Name = document.getElementById("Last_Name").value;
var Age = document.getElementById("Age").value;
window.external.finished(First_Name + "," + Last_Name + "," + Age);