aqui está um exemplo de formulário com preenchimento automático, você pode usar localstorage
<input id="FirstName" type="text" name="FirstName" class="field-style" placeholder="First Name" required onchange="save()"/>
<script>
// Check browser support
if (typeof(Storage) !== "undefined") {
if(localStorage.getItem("FirstName")!=""){
}else{
// Store
localStorage.setItem("FirstName", "Hitesh");
}
// Retrieve
document.getElementById("FirstName").value = localStorage.getItem("FirstName");
} else {
document.getElementById("FirstName").value = "Sorry, your browser does not support Web Storage...";
}
function save(){
var name = document.getElementById('FirstName').value;
localStorage.setItem("FirstName", name);
}
</script>
