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Past participles are used for all perfect tense forms of a verb and in the passive voice in English. For regular verbs, we normally add ED to form its past participle. Unfortunately for irregular verbs there are no rules and it is just a matter of practice. The highlighted words or words in bold below are examples of past participles:
1. Present perfect
She hasn't finished her assignment yet.
I still haven't found my keys.

2. Past perfect
Chris was ill because he had eaten too much chocolate.
She missed the bus because she hadn't set her alarm.

3. Future perfect
Jamie will have been in Australia for one year in April.
He will have gone by the time you arrive.

4. Conditional perfect
If his passport had not been stolen, Adam would have gone to Brazil.
I wouldn't have known if you hadn't told me.

5. Passive Voice
The west coast of The USA was struck by torrential rain last night.
The painting was stolen in the middle of the night.

Participles as adjectives Past Participles can also be used like an adjective in front of a noun:
The stolen baby was found by the police unharmed.
Dean's broken arm was set in plaster by the doctor at the hospital.
Please bring all of the required documents for your interview tomorrow.
past participles are used in the passive forms and in all perfect tense forms to which ed or en is added
 hope it helps....