public static string FileName = "test.txt";
public static void Main()
string urlString = "http%3a%2f%2ftest%23+space+123%2ftext%3fvar%3dval%26another%3dtwo";
var bytes = urlString.UrlDecodeToBytes();
var file = FileName.ToFileInfo();
file.WriteAllBytes(bytes);
Console.WriteLine(file.ReadAllText());