C#

please short I remember that when clicking in a cell that the corresponding date evening retrieve and store in a variable. I use a calendar layout like a tables or columns are dates and a column has several cells, I want when I click on a cell to get its corresponding date.
I program in c #

List<string> documents = new List<string>();

private async void btnConvert_Click(object sender, EventArgs e)
{
    using (var client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true }))
    {
        client.BaseAddress = new Uri(BaseApiUrl);
        //client.DefaultRequestHeaders.Add("Accept", "application/json");

        // Add an Accept header for JSON format.
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, BaseApiUrl + ApiUrl);

        foreach (string s in docPaths)
        {
            byte[] bte;
            bte = File.ReadAllBytes(docPath);

            string data = JsonConvert.SerializeObject(Convert.ToBase64String(bte));
            documents.Add(data);
        }

        using (var formData = new MultipartFormDataContent())
        {
            foreach (string s in documents)
            {
                //add content to form data
                formData.Add(new StringContent(s, Encoding.UTF8, "application/json"));
            }

            // List of Http Reponse Messages
            var conversions = documents.Select(doc => client.PostAsync(BaseApiUrl + ApiUrl, formData)).ToList();

            //Wait for all the requests to finish
            await Task.WhenAll(conversions);

            //Get the responses
            var responses = conversions.Select
                (
                    task => task.Result
                );

            foreach (var r in responses)
            {
                // Extract the message body
                var s = await r.Content.ReadAsStringAsync();
                SimpleResponse res = JsonConvert.DeserializeObject<SimpleResponse>(s);

                if (res.Success)
                {
                    byte[] pdf = Convert.FromBase64String(res.Result.ToString());

                    // Save the PDF here
                }
                else
                {
                   // Log issue
                }
            }
        }
    }

[HttpPost]
public async Task<List<SimpleResponse>> Post([FromBody]string request)
{
    var response = new List<SimpleResponse>();
    AIMSConverter convert = new AIMSConverter();

    var provider = new MultipartMemoryStreamProvider();
    await Request.Content.ReadAsMultipartAsync(provider);
    foreach (var requestContents in provider.Contents)
    {
        try
        {
            //var result = convert.CovertDocToPDF(requestContents, WebConfigurationManager.AppSettings["tempDocPath"], WebConfigurationManager.AppSettings["tempPdfPath"]);

            //response.Add(new SimpleResponse() { Result = result, Success = true });
        }
        catch (Exception ex)
        {
            response.Add(new SimpleResponse() { Success = false, Exception = ex, Errors = new List<string>() { string.Format("{0}, {1}", ex.Message, ex.InnerException?.Message ?? "") } });
        }
    }

    return response;
}

public class SimpleResponse
{
    public object Result { get; set; }
    public bool Success { get; set; }
    public Exception Exception { get; set; }
    public List<string> Errors { get; set; }
}