How to close a firm under income tax

I think there is no such procedure in the income tax act.

But in case of partnership firm, you can dissolve the firm & send the copy of deed with appropriate forwarding letter to the assessing officer for knowledge that the firm is now closed.

There is no provision to surrender PAN in case you have only one PAN. Also your firm can be chosen for scrutiny under IT act in future even after dissolution. So in my openion, the PAN wont be cancelled. But by initmation to AO about closure of firm may save you for future from violation of provisions of income tax act.