EWS is a Central Government Reservation that is for Candidates who belong to General Category and whose annual income from all sources is less than 8 lakhs per annum. It is across Academic and Employment sectors. It is 10% across all sectors.  An EWS Certificate issued by a local authority with duly signed and attested is good and considered authentic enough. Even if it is at Tehsildar or SDO level, it is still considered good.
You will need 3 documents:

1. DOCUMENTS FOR DATE OF BIRTH: You have to provide any of the mentioned documents as said above in the article body.

*Birth certificate under the Birth. Death and Marriage Certificate Act. 1969.

*Hospital/Auxiliary urse and Midwife.(ANM) register record.

*Anganwadi Record.

*Declaration of age of the child by the parents or guardian.

2. DOCUMENTS FOR PROOF OF PRESENT RESIDENTIAL ADDRESS:-

*Ration card in the name of Parents having name of the Child in Ration card.

*Domicile certificate of child or his/her parents.. .

*Voter Id card of any of the parents.

*Electricity Bill/MTNL telephone bill/Water bill.

*Unique Identity Card (Aadhar) of Mother/Father/Child issued by Govt. of India.

*Passport in the name of any of the parents or child

3. DOCUMENTS FOR PROOF OF ECONOMICALLY WEAKER SECTION (EWS):-

*Income. certificate issued by ae Revenue Officer not below the rank of Tehsildar

*BPL Ration Card (Yellow coloured)

*AAY Ration Card (pink coloured)

*Food Security card.issued by Food & supply Dept.(GNCT of Delhi)
With these documents you can prove that you belong to EWS category.