Simplest way:
Process.Start(@"D:\Test Data\APage.html");
Or:
Process.Start(@"https://www.codeproject.com/Questions/5286855/How-do-I-open-Google-chrome-in-Csharp");
But if Chrome isn't the default browser, you need to be more specific:
Process.Start("chrome.exe", @"https://www.codeproject.com/Questions/5286855/How-do-I-open-Google-chrome-in-Csharp");
And opening a file is more complex too:
Process.Start("chrome.exe", @"file://D:\Test%20Data\APage.html");