As you have sold our property, you need to keep the following documents (photocopies off course as original must have transferred to the buyer) in your record for Income Tax purposes & otherwise: -
a) Agreement to Sale
b) Power of attorney
c) Conveyance Deed
d) Certificate/Deed from DDA if it was a leasehold property or freehold property certificate
e) Proof of payment of stamp duty, which you must have paid at the time of purchase of your property
f) All the bills of expenditures incurred for the renovation, repair & maintanence of your house.
g) House Tax payment, electricty & water bills payment proof
h) NOC from your society for no dues pending, if applicable
i) All records of receipt of consideration through Bank & otherwise
j) Proof of making investment for claiming exemption U/s 54 etc , if applicable
Docx for purchase of new Property: -
You should not presume that your property dealer would provide you all the necessary documents automatically, you need to ensure yourself whether you have all the papers required to you or not.