有很多答案，但这是我最近使用的。net 6或更高版本的解决方案。

using var httpClient = new HttpClient();

var tempPath = Path.GetTempFileName();

await using var s = await HttpClient.GetStreamAsync(pdfFilePath);

await using var fs = File.OpenWrite(tempPath);

await s.CopyToAsync(fs);

使用GetIsNetworkAvailable()检查网络连接，以避免在未连接到网络时创建空文件。

if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
{
    using (System.Net.WebClient client = new System.Net.WebClient())
    {                        
          client.DownloadFileAsync(new Uri("http://www.examplesite.com/test.txt"),
          "D:\\test.txt");
    }                  
}

试试这个:

private void downloadFile(string url)
{
     string file = System.IO.Path.GetFileName(url);
     WebClient cln = new WebClient();
     cln.DownloadFile(url, file);
}

你也可以在WebClient类中使用DownloadFileAsync方法。它将具有指定URI的资源下载到本地文件。此外，此方法不会阻塞调用线程。

示例:

    webClient.DownloadFileAsync(new Uri("http://www.example.com/file/test.jpg"), "test.jpg");

欲了解更多信息:

http://csharpexamples.com/download-files-synchronous-asynchronous-url-c/

下面的代码包含下载文件的逻辑与原始名称

private string DownloadFile(string url)
    {

        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
        string filename = "";
        string destinationpath = Environment;
        if (!Directory.Exists(destinationpath))
        {
            Directory.CreateDirectory(destinationpath);
        }
        using (HttpWebResponse response = (HttpWebResponse)request.GetResponseAsync().Result)
        {
            string path = response.Headers["Content-Disposition"];
            if (string.IsNullOrWhiteSpace(path))
            {
                var uri = new Uri(url);
                filename = Path.GetFileName(uri.LocalPath);
            }
            else
            {
                ContentDisposition contentDisposition = new ContentDisposition(path);
                filename = contentDisposition.FileName;

            }

            var responseStream = response.GetResponseStream();
            using (var fileStream = File.Create(System.IO.Path.Combine(destinationpath, filename)))
            {
                responseStream.CopyTo(fileStream);
            }
        }

        return Path.Combine(destinationpath, filename);
    }

在.NET Core MVC中，你有时可以简单地这样做:

public async Task<ActionResult> DownloadUrl(string url) {
    return Redirect(url);
}

这可能假设您正在尝试下载的MIME类型被浏览器设置为可下载(例如.mp4)，因此它不会尝试重定向到网页。