Is it possible to file income tax returns on behalf of another person?

Yes you can file the tax on behalf of another person. However it is helpful for that person and yourself if you open the account on IT dept website. And also link his PAN number with that account. Registering his account on the website and verifying with the phone number helps with the confirmation.

You need following things :

1. Total revenue earned (salary or business) in excel sheet.
2. PDF or printout of bank account statements.
3. Deductible statements (e.g. PPF, health insurance and other deductibles)

Once you make calculations of the amount of money to be paid by tax, just go ahead and file the chalan for him from his bank account.

I suggest instead of going through all the things yourself, pay the CA to do this for you. It saves you time and also the complications.

Yes you can do that. You will need to create a account on IT Dept site on the behalf of that person.

You will need : -
1. Revenue Figures
2. Statement from Bank or from the place where he works.
Deductible statements are not important but will needed if he applied for any health insurance, etc.

After collecting all these just sign up and upload all these stuff, calculate the amount of tax to be paid by that certain person and file the chalan.

Well, it is possible to file income returns for your friend. But for for the purpose, you will need to have all his account credentials. You will need to link his PAN card details to the account on IT site.
You will need to have his netbanking details ( or the credit/debit card card information). It may not be a practically well thought of decision.
As per the law, only legal heirs of a deceased individual can file the returns of the person till the transfer of assets is done.
However, if still you need to do it - you will need following details -

1. The details of the revenue for the filing period

2. Bank statements

3. Deductible accounts if any.