There is no past participle. The idiomatic construction "have to" means "must" and is used as an auxiliary verb. (The verb to have has the past tense had and the past participle had.)
The past participle of do is done. The past participle of have is had.
The past participle of am is been. Not does not have a past participle
What is the past participle of do
The past participle of have is had....:) I have had...
The past participle is been.
The past participle is willed.
The past participle is had.
Being is the present participle. The past participle is been.
The past participle is thought.
To isn't a verb and so doesn't have a past participle. The past participle of be is been.
The past tense and the past participle is "answered".
The present participle is hiding.The simple past tense is hid.The past participle is hidden.