You could load a single page as
FileStream source = new FileStream(filepath, FileMode.Open, FileAccess.Read);
webBrowser1.DocumentStream = source;
or even like
string html = File.ReadAllText(filepath);
webBrowser1.DocumentText = html;
But if you have images, css or js in the relative paths, use
Uri uri = new Uri(filepath);
webBrowser1.Navigate(uri);
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…