Is there any document to be enclosed along with refund claim? If yes, what are the documents to be submitted

Yes, the following documents are required to be enclosed along with the refund application:
1. Documentary evidence to establish that a refund is due to the applicant
(prescribed under Rule 89(2) of the CGST Rules, 2017, and
2. Documentary evidence to prove that incidence of tax and interest had not been passed on to any other person.

(ICAI FAQ PUBLICATIONS 06-09-2017 REFUNDS: FAQ NO. 13)