在C#中，使用Newtonsoft.Json庫處理復雜對象非常簡單。首先，確保已經安裝了Newtonsoft.Json NuGet包。然后，按照以下步驟操作：

1. 定義一個復雜對象類。例如，我們有一個包含員工信息的Employee類：

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Address Address { get; set; }
}

public class Address
{
    public string Street { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }
}

2. 使用Newtonsoft.Json庫將對象序列化為JSON字符串：

using Newtonsoft.Json;

Employee employee = new Employee
{
    Id = 1,
    Name = "John Doe",
    Address = new Address
    {
        Street = "123 Main St",
        City = "Anytown",
        State = "CA",
        ZipCode = "12345"
    }
};

string jsonString = JsonConvert.SerializeObject(employee);
Console.WriteLine(jsonString);

這將輸出以下JSON字符串：

{"Id":1,"Name":"John Doe","Address":{"Street":"123 Main St","City":"Anytown","State":"CA","ZipCode":"12345"}}

3. 使用Newtonsoft.Json庫將JSON字符串反序列化為復雜對象：

string jsonString = "{\"Id\":1,\"Name\":\"John Doe\",\"Address\":{\"Street\":\"123 Main St\",\"City\":\"Anytown\",\"State\":\"CA\",\"ZipCode\":\"12345\"}}";

Employee employee = JsonConvert.DeserializeObject<Employee>(jsonString);
Console.WriteLine($"Id: {employee.Id}, Name: {employee.Name}, Address: {employee.Address.Street}, {employee.Address.City}, {employee.Address.State}, {employee.Address.ZipCode}");

這將輸出：

Id: 1, Name: John Doe, Address: 123 Main St, Anytown, CA, 12345

通過這些步驟，您可以在C#中使用Newtonsoft.Json庫處理復雜對象。