No documents are needed at any point during the census. Census documents required India is essentially a trick question because the answer is zero! You don't need ID proofs, Aadhaar, passports, or anything. Self-enumeration and physical enumeration both require zero documentation.
The census is about counting people and their circumstances, not verifying identity through papers. Simply provide verbal information about your household composition, education, occupation, and living conditions. This makes it incredibly accessible for marginalized communities without formal documents.