Padma Purana is one of the eighteen principal Puranas, as explained in the Shirmad-Bhagavatam (12.7.25):

“The eighteen major Puranas are the Brahma, Padma, Vishnu, Shiva, Linga, Garuda, Narada, Bhagavata, Agni, Skanda, Bhavishya, Brahma-vaivarta, Markandeya, Vamana, Varaha, Matsya, Kurma and Brahmanda Puranas.”

It is further explained that six of these Puranas are considered to be for those in the mode goodness, six are for those in passion, and six are for those in ignorance. The Padma Purana is one of the six for those in goodness.