This is more Pakistani paranoia than anything else. Maybe it is the narrative that the Pakistani military establishment wants you to believe to ensure its popularity and power they enjoy in Pakistan - that India never really accepted Pakistan's existence and is constantly looking for an opportunity to invade and annex Pakistan into its own territory.
Annexing Pakistan, laughable as it sounds, into Indian territory will cause a lot more problems for India in terms of civil strife, religious riots, fundamentalism and extremism on both sides and it will essentially be a throwback to the good, sorry, bad old days of the partition. India has already a lot of problems like poverty, overpopulation, income inequality, illiteracy etc., to deal with on its own and has only made improvements in the recent decades. Religious strife, civil war and extremism would put the years of development, whatever it did so far, to waste. If India wanted to annex Pakistan so badly, how many wars did it start to initiate that process. Or why did it not annex East Pakistan after it was liberated. Or simply use common sense - if the Indian political class hate muslims so much, why would they deliberately choose to annex an almost entirely muslim country to its population, thereby raising the muslim population in the country?
