[Parameter]
public bool ViewMergedData { get; set; }

@inject NwindDataService NwindDataService
<DxRichEdit>
    <MailMergeSettings>
        <DxMailMergeSettings Data="@DataSource" ViewMergedData="true" ActiveRecord="1"/>
    </MailMergeSettings>
</DxRichEdit>

@code {
    IEnumerable<Employee> DataSource;
    protected override async Task OnInitializedAsync() {
        DataSource = await NwindDataService.GetEmployeesAsync();
        await base.OnInitializedAsync();
    }
}

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
namespace BlazorDemo.Data.Northwind {
    public partial class Employee {
        public Employee() {
            this.Orders = new List<Order>();
        }
        public int EmployeeId { get; set; }
        public string LastName { get; set; }
        public string FirstName { get; set; }
        public string Title { get; set; }
        public string TitleOfCourtesy { get; set; }
        public Nullable BirthDate { get; set; }
        public Nullable HireDate { get; set; }
        public string Address { get; set; }
        public string City { get; set; }
        public string Region { get; set; }
        public string PostalCode { get; set; }
        public string Country { get; set; }
        public string HomePhone { get; set; }
        public string Extension { get; set; }
        public string Notes { get; set; }
        public Nullable<int> ReportsTo { get; set; }
        public string PhotoPath { get; set; }
        public virtual ICollection<Order> Orders { get; set; }
        public string Text => $"{FirstName} {LastName} ({Title})";
        public string ImageFileName => $"Employees/{EmployeeId}.jpg";
    }
}