Why are the documents required for HDFC Credit Card and do they need physical verification?

If I apply for a credit card in HDFC, do they send someone to verify your address? Also, wanted to know what all original documents are required so I keep them available to not delay the process.

Not only HDFC, almost all banks require physical verification. It is done to check and approve your application. Banks require 3 types of proof: Identity, Address and Income.
These include any of PAN Card, Aadhaar Card, Driver’s License, Passport; utility bills, bank statements, latest salary slips, ITR whichever they request for. Mostly it’s among these docs.

You’re right, having them docs prepared helps in little to no delay. You can refer to the link for more info:
Credit Cards FAQs > docs required