Is had a past particle

Answer 1

While it probably does sound like "particle" if you are just learning English grammar, the word is "participle". The verb "to have" is a helping verb; it can be used with a present or a past participle. For example: I have spoken with my sister. ("have" is the helping verb, "spoken" is the participle). He had seen a lot of coats before he found the one he liked ("had" is the helping verb, showing a past action; "seen" is the past participle). So, to sum up, "had" is not a participle, but can be used in a sentence where there is a participle.