An Advocate is not barred from making and filing income tax returns for the client on client's signature. But check with IT department/ Auditors, whether Advocates are allowed to file e-return of their clients with their own signature.

Of course tax can be paid by you and got reimbursed. If there is Advance Tax due, then it is the obligation of the client only.

1)You may file returns either manually or efiling but not allowed to sign on behalf of your clients using your digital signature account.

2)You cannot pay tax on behalf of your client using your debit/credit cards,as this deed may amount to misrepresentation because you have not mentioned that you are filing in the status of representative assessee.Moreover if you pay the taxes you have to account the amount of taxes paid on behalf of your clients and would have to be treated as a loan.In the same manner the transaction would be shown as loan taken for paying taxes from your account.