How to manage reports within application using Bold Reports Report Designer?

You can use ExternalServer to manage the reports with in application. Find the following code for accessing the existing reports, datasources and datasets from application App_Data folder.

public override List<CatalogItem> GetItems(string folderName, ItemTypeEnum type)
        {
            List<CatalogItem> _items = new List<CatalogItem>();
            string targetFolder = HttpContext.Current.Server.MapPath("~/") + @"App_Data\ReportServer\";

            if (type == ItemTypeEnum.Folder || type == ItemTypeEnum.Report)
            {
                targetFolder = targetFolder + @"Report\";
                if (!(string.IsNullOrEmpty(folderName) || folderName.Trim() == "/"))
                {
                    targetFolder = targetFolder + folderName;
                }
            }

            if (type == ItemTypeEnum.DataSet)
            {
                foreach (var file in Directory.GetFiles(targetFolder + "DataSet"))
                {
                    CatalogItem catalogItem = new CatalogItem();
                    catalogItem.Name = Path.GetFileNameWithoutExtension(file);
                    catalogItem.Type = ItemTypeEnum.DataSet;
                    catalogItem.Id = Regex.Replace(catalogItem.Name, @"[^0-9a-zA-Z]+", "_");
                    _items.Add(catalogItem);
                }
            }
            else if (type == ItemTypeEnum.DataSource)
            {
                foreach (var file in Directory.GetFiles(targetFolder + "DataSource"))
                {
                    CatalogItem catalogItem = new CatalogItem();
                    catalogItem.Name = Path.GetFileNameWithoutExtension(file);
                    catalogItem.Type = ItemTypeEnum.DataSource;
                    catalogItem.Id = Regex.Replace(catalogItem.Name, @"[^0-9a-zA-Z]+", "_");
                    _items.Add(catalogItem);
                }
            }
            else if (type == ItemTypeEnum.Folder)
            {
                foreach (var file in Directory.GetDirectories(targetFolder))
                {
                    CatalogItem catalogItem = new CatalogItem();
                    catalogItem.Name = Path.GetFileNameWithoutExtension(file);
                    catalogItem.Type = ItemTypeEnum.Folder;
                    catalogItem.Id = Regex.Replace(catalogItem.Name, @"[^0-9a-zA-Z]+", "_");
                    _items.Add(catalogItem);
                }
            }
            else if (type == ItemTypeEnum.Report)
            {
                foreach (var file in Directory.GetFiles(targetFolder, "*.rdl"))
                {
                    CatalogItem catalogItem = new CatalogItem();
                    catalogItem.Name = Path.GetFileNameWithoutExtension(file);
                    catalogItem.Type = ItemTypeEnum.Report;
                    catalogItem.Id = Regex.Replace(catalogItem.Name, @"[^0-9a-zA-Z]+", "_");
                    _items.Add(catalogItem);
                }
            }

            return _items;
        }

You can refer the below application for using the ExternalServer ExternalServer Sample