MultipartFormBuilder.cs

internal class MultipartFormBuilder
    {
        private MultipartFormDataContent _form = new();

        public MultipartFormBuilder()
        {

        }

        internal MultipartFormBuilder AddDocument(Document document)
        {
            var fileContent = new ByteArrayContent(document.Data);
            fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse(document.Format);
            _form.Add(fileContent, "documents", document.Name);

            return this;
        }

        internal MultipartFormDataContent Build()
        {
            return _form;
        }
    }