Introduction:
In this task, we are required to change the voice of the given sentence from active to passive voice. The given sentence is "Pappu laughed at me." To convert this sentence into passive voice, we need to follow specific rules and guidelines.

Explanation:
To transform the given sentence from active to passive voice, we can use the following steps:

Step 1: Identify the subject and the object:
The subject of the sentence is 'Pappu', and the object is 'me'.

Step 2: Determine the tense and form of 'to be':
In this case, the verb 'laughed' is in the past tense. Therefore, we will use the past tense of 'to be', which is 'was/were', depending on the subject.

Step 3: Form the passive voice sentence:
To convert the active voice sentence into passive voice, we place the object of the active sentence as the subject in the passive sentence. The subject of the active sentence becomes the agent in the passive sentence (if mentioned). The verb 'laughed' becomes the past participle 'laughed'. The preposition 'at' is usually omitted in passive constructions.

Following these steps, we can transform the given sentence into passive voice:
"I was laughed at by Pappu."

Conclusion:
In conclusion, the active sentence "Pappu laughed at me" has been transformed into the passive sentence "I was laughed at by Pappu." By following the mentioned rules and guidelines, we successfully changed the voice of the sentence while maintaining its meaning.

Active voice: Pappu laughed at me.