Why are companies asking for pan, Aadhar and salary slips for offer letter?

Recently interviewed and got the job but HR asked all the documents before generating an offer. I was surprised they asked for these documents upon asking HR said it’s for verification- however I told them it’s more like technique to negotiate on CTC. I don’t have problem with background verification but just don’t seem to share my details even before the offer. Did you face something similar and received offer without it?