Stimulsoft PDF Forms provides an Angular component for editing and filling forms in the browser, backed by a single ASP.NET Core action.

Handle form requests in the controller.
[HttpPost]
public IActionResult Action()
{
    var data = JObject.Parse(this.HttpContext.Request.Form["data"]);
    var action = data["action"].ToString();
    switch (action)
    {
        case "Initialize":
            var initData = StiWebForm.Initialize(data, null);
            return Json(initData.Content);
        default:
            var result = StiWebForm.ProcessRequest(data);
            return result.ContentType switch
            {
                "application/pdf" => new FileContentResult(result.Content as byte[], result.ContentType),
                _ => Json(result.Content),
            };
    }
}

How it works. A single action multiplexes the form component's requests, so the Angular form talks to one endpoint for setup, editing and PDF output.