var pdf_filename = "Path to pdf";

            //field names will be stored in this list.

            var fieldList = new List<string>();

            using (var reader = new PdfReader(pdf_filename))

            {

                var fields = reader.AcroFields.Fields;

​

                foreach (var key in fields.Keys)

                {

                    var value = reader.AcroFields.GetField(key);

                    fieldList.Add(key + " : " + value);

                }

            }

            Console.Writeline(fieldList);//Print list of pdf field names