I find Paramatman an intriguing concept, but I'm struggling to understand how it relates to Atman and Brahman - it is a sort of unifying concept? Can anyone provide a simple explanation?
https://en.wikipedia.org/wiki/Paramatman
Nitaibol. It really depends on the school in how the Paramatma is explained and its relationship with Atman and Brahma. Kiranji and Aupmanyavji have already explained the Adwaita position, I will briefly explain the Vaishnav (specifically Gaudiya) view:
For us, Paramatma refers to the Supersoul which is considered to be the partial expansion of God (specifically known as
Ksirodaksayi Visnu). The Paramatma has 2 main functions. Its first function is that it resides alongside the Jiva-atma in the body of every single living entity, bestowing upon the Jiva-atma the fruit of its
karma. Its second function is that the Paramatma pervades (and is within) every single atom within material creation, acting as its support. Vaishnavs cite the following verse from Mundaka Upanisad 3.1.1-2 in support of this:
dvā suparṇā sayujā sakhāyā
samānaṁ vṛkṣaṁ pariṣasvajāte
tayor anyaḥ pippalaṁ svādy atty
anaśnann anyo 'bhicākaśīti
"There are two birds in one tree. One of them (the Jivatma) is eating the fruits of the tree, while the other (paramatma) is witnessing the actions. The witness is the Lord, and the fruit-eater is the living entity."
samāne vṛkṣe puruṣo nimagno
'nīśayā śocati muhyamānaḥ
juṣṭaṁ yadā paśyaty anyam īśam
asya mahimānam iti vīta-śokaḥ
"Although the two birds are in the same tree, the eating bird is fully engrossed with anxiety and moroseness as the enjoyer of the fruits of the tree. But if in some way or other he turns his face to his friend who is the Lord and knows His glories—at once the suffering bird becomes free from all anxieties."
Based upon our interpretation of the above verse, there is a permanent different between the Jivatma (self) and the Paramatma. The Paramatma is a partial expansion of Lord Sankarshana (Visnu) while the Jivatma is a fragmented fraction of the impersonal Brahman.