A participle has the form of verb + -ing. So the only such word here is 'smiling' that is the participle in this sentence. It modifies 'woman', that is, it refers to how the woman opened the door - smiling pleasantly.
American Farmland trust work to protect the soil and keep it healthy as part of our holistic approach to keeping the nation's farm and ranch land productive for all and it educates Farmers on important conservation measures like cover crops.
