CSHARP

process.start web

System.Diagnostics.Process.Start("http://www.webpage.com");

Process start web document

System.Diagnostics.Process process = new System.Diagnostics.Process();
try
{
    process.StartInfo.UseShellExecute = true;
    process.StartInfo.FileName = pathToHtmlFile;
    process.Start();
}
catch (Exception e)
{
    Console.WriteLine(e.Message);
}