No, the word overjoyed is not an adverb.The word overjoyed is an adjective.
overjoyed
She was overjoyed to see the boy.
The root word for "overjoyed" is "joy." The prefix "over-" is added to intensify the feeling of joy.
i was overjoyed when my team won the trophy
My dog is normally overjoyed to see me.
elated
yes
yes
· overjoyed
frantic overjoyed
overjoyed