HeroCard

MainBot.cs

// Reply to the activity we received with an activity.
var reply = turnContext.Activity.CreateReply();

var heroCard = new HeroCard
{
    Title = "BotFramework Hero Card",
    Subtitle = "Microsoft Bot Framework",
    Text = "Build and connect intelligent bots to interact with your users naturally wherever they are," +
           " from text/sms to Skype, Slack, Office 365 mail and other popular services.",
    Images = new List<CardImage> { new CardImage("https://sec.ch9.ms/ch9/7ff5/e07cfef0-aa3b-40bb-9baa-7c9ef8ff7ff5/buildreactionbotframework_960.jpg") },
    Buttons = new List<CardAction> { new CardAction(ActionTypes.OpenUrl, "Get Started", value: "https://docs.microsoft.com/bot-framework") },
};

reply.Attachments.Add(heroCard.ToAttachment());

// Send the card(s) to the user as an attachment to the activity
await turnContext.SendActivityAsync(reply, cancellationToken);