Passive Voice

Passive voice is called Karmani prayoga in Sanskrit.

The sentence
        Radha reads a book.
is in active voice.

When we convert it to passive voice it becomes
      A book is read by Radha.

How is that accomplished in Sanskrit?

The subject should be written in Tritiya vibhakti - instrumental case. And the object is written in prathama vibhakti - nominative case.

Active voice   kartari prayoga - राम​: पाठं पठति ।

Passive voice - karmani prayoga - रामेन पाठ​: पठ्यते |

Here the verb पठ्यते follows the case, number and gender of object (karma) - पाठ​:

If Rama reads multiple lessons - plural, then the sentences will be

Active voice   kartari prayoga - राम​: पाठान् पठति ।

Passive voice - karmani prayoga - रामेन पाठानि पठ्यन्ते  |

The verb  पठ्यन्ते is in plural in passive voice because पाठानि is plural.

Let us write some more examples .

Kartari                                                            Karmani

मुनि: मोहं त्यजति ।                                             मुनिना मोहम् त्यज्यते ।
बालक​: फलं भक्षयति ।                                         बालकेन फलं भक्ष्यते ।

बालिका प्रश्नं प्रच्छति |                                    बालिकया प्रश्न​: प्रच्छ्यते |           

Let us look at the present tense forms of the verb पठ                           

आत्मनेपदे	एक	द्वि	बहु
प्रथम	पठते	पठेते	पठन्ते
मध्यम	पठसे	पठेथे	पठध्वे
उत्तम	पठे	पठावहे	पठामहे