How to send user a CSV file which is created by bot C# BotFramework SDK3

If your CSV file is stored in your project folder, to send a CSV file to the user(s), you can refer to the following sample code.

var replymes = context.MakeMessage();
replymes.Text = "Here is a CSV file.";

replymes.Attachments.Add(await GetCSVAttachmentAsync(replymes.ServiceUrl, replymes.Conversation.Id));

await context.PostAsync(replymes);

The implementation of GetCSVAttachmentAsync:

private static async Task<Attachment> GetCSVAttachmentAsync(string serviceUrl, string conversationId)
{
    var filePath = System.Web.HttpContext.Current.Server.MapPath(@"~\csv_files\userinfo.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 = "userinfo.csv",
                OriginalBase64 = System.IO.File.ReadAllBytes(filePath),
                Type = "text/csv"
            });

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

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

Test result:

Update:

Store the CSV file in Azure storage blob, and send it as attachment.

var storageAccount = CloudStorageAccount.Parse("{storage_connection_string}");

var blobClient = storageAccount.CreateCloudBlobClient();
var cloudBlobContainer = blobClient.GetContainerReference("mycontainer");
cloudBlobContainer.CreateIfNotExists();

var cloudBlockBlob = cloudBlobContainer.GetBlockBlobReference("userinfo.csv");

cloudBlockBlob.UploadFromFile(System.Web.HttpContext.Current.Server.MapPath(@"~\csv_files\userinfo.csv"));

var url = cloudBlockBlob.Uri.ToString();

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