How to send attachment in bot framework in web embedded bot using c#

You can achieve this using a herocard. The problem with your code is that you are not specifying the filename along with the location i.e if your filename is ProjectFile then the value in the button must contain ProjectFile.csv

The best approach is to add the file to a folder in your project and add the reference in the value of the Card Action in the button.

eg:

    Attachment attachment = new HeroCard
    {
        Title = "Click to download Report",
        Buttons = new List<CardAction>()
        {
            new CardAction()
            {
                Title = "Get Started",
                Type = ActionTypes.OpenUrl,
                Value = "D:\\ProjecteFile\\Results.csv"
            }
         }
    }.ToAttachment();

    var reply = context.MakeMessage();
    reply.Attachments.Add(attachment);
    await context.PostAsync(reply);

It seems that your csv file is stored in your project folder and you’d like to send it as attachment from your bot to web client user. I use Attachments API to upload it and then send it to user, which works for me, you can refer to it.

Get uploaded attachment and send to user:

var replymes = context.MakeMessage();

Attachment attachment = null;
attachment = await GetUploadedAttachmentAsync(replymes.ServiceUrl, replymes.Conversation.Id);

replymes.Attachments.Add(attachment);

await context.PostAsync(replymes); 

GetUploadedAttachmentAsync:

private static async Task<Attachment> GetUploadedAttachmentAsync(string serviceUrl, string conversationId)
{
    var imagePath = System.Web.HttpContext.Current.Server.MapPath(@"~\csv_files\Results.csv");

    using (var connector = new ConnectorClient(new Uri(serviceUrl)))
    {
        var attachments = new Attachments(connector);
        var response = await attachments.Client.Conversations.UploadAttachmentAsync(
            conversationId,
            new AttachmentData
            {
                Name = "Results.csv",
                OriginalBase64 = File.ReadAllBytes(imagePath),
                Type = "text/csv"
            });

        var attachmentUri = attachments.GetAttachmentUri(response.Id);

        return new Attachment
        {
            Name = "Results.csv",
            ContentType = "text/csv",
            ContentUrl = attachmentUri
        };
    }
}

Test in Web Chat:

Note: as far as I know, specify the path of the file that is stored in local folder or shared network folder and directly send as attachment to user, which are not supported in bot.

protected override async Task OnMessageActivityAsync(ITurnContext<IMessageActivity> turnContext, CancellationToken cancellationToken)
    {
        //img and excel is special keyword which provide image or excel
        //Get message reply use getmsg method
        switch (turnContext.Activity.Text)
        {
            case "img":
                await turnContext.SendActivityAsync(MessageFactory.Attachment(GetImg()), cancellationToken);
                break;
            case "excel":
                await turnContext.SendActivityAsync(MessageFactory.Attachment(GetImg()), cancellationToken);
                break;
            default:
                await turnContext.SendActivityAsync(MessageFactory.Text(GetMsg(turnContext.Activity.Text)), cancellationToken);
                break;
        }

    }

    private Attachment GetImg()
    {
        var imagePath = Path.Combine(Environment.CurrentDirectory, @"bin\Debug\img.png");
        var imageData = Convert.ToBase64String(File.ReadAllBytes(imagePath));

        return new Attachment
        {
            Name = @"img.png",
            ContentType = "image/png",
            ContentUrl = $"data:image/png;base64,{imageData}",
        };
    }