According the the Instrument of Accession (Jammu and Kashmir) signed by the ruler of the princely state of Jammu and Kashmir, Maharaja Hari Singh, the entire state of Jammu and Kashmir is a part of India, Gilgit-Balitistan included.
Tribal invaders sponsored by the Pakistani army then invaded the northwestern parts of Jammu and Kashmir, known as Azad Kashmir and Gilgit-Balitistan. The region has been illegally occupied by Pakistan ever since. The Line of Control is between India and Pakistan.
Acording to UNSC Resolution of 1947 the territory is part of the disputed Kashmir
Then how pakistan can make administrative in that area ?