controller.cs

[HttpGet]
public IActionResult Template([FromQuery] TemplateRequest templateRequest)
{
    // create a ReportingCloud object with stored API-Key
    ReportingCloud rc = new ReportingCloud(RCSettings.APIKey);

    // download document from ReportingCloud template storage
    byte[] document = rc.DownloadTemplate(templateRequest.TemplateName);

    // return Base64 string version
    return new OkObjectResult(Convert.ToBase64String(document));
}