
What to do if you’re buying apartment in cash?
Hey did anyone bought apartment in full cash? For example does the sale deed need to be in stamp paper?

Apartments can definitely be bought in an all cash transaction.
As long as the cost of the apartment is < 2 Lac.
Section 269ST of the Income Tax Act prohibits any person from accepting cash over Rs.2 lakh from a single person and in a single day, or in respect of multiple transactions received from a single person that relates to a single event or occasion.
Also, registration is the legal method for transfer of ownership & title. Why would you want to avoid stamp & registration?

Okay, my question is wrong. I mean to say if I buy via cheque then what different document or change in sale deed? For eg does sale agreement should be on the stamp paper if no loan needed?

Everything needs to be registered.
The only way to register a deed is to pay stamp to the state.
So, Yes - Stamp is necessary and never optional.