As you asked in your question that your wife has a PAN Number but does not have any income then its means that there is no any need to file the return of income in this case as you mentioned. However in many cases we have to file the return of income and one of that is if we filed the return of income in last year i.e. if we have filed our return of income in last year or once we start a filling a return, in this case we have to file the return of income whether we have any income from any source or not.
Now the procedure of filling the income tax return is given below:
There are many types of ITR(Income Tax Return) which we have to filled with departments
Let suppose ITR-4 This ITR relates with business or profession's income.
As like you your wife have any income example bank interest, interest on FD, tuition income etc. then your wife will have to file the return of income and in this case your wife should disclose her income in form ITR-1 or ITR-2.
If your wife has any salary income then in this case also your wife should file the return of income in above mentioned ITR forms.
If your wife has a business income or any professional income suppose your wife is a doctor or lawyer, in this case your wife should file a return in form ITR-4.
However the basic limit for AY 2018-19 for individuals is Rs. 2,50,000/- i.e. up to Rs. 2,50,000/- (net income) there is no any tax and after from 2,50,000/- to 5,00,000/- there is only 5% tax on income.
Here net income means the income which is arrive or calculated after deduction of chapter VIA i.e. deductions under section 80C, 80TTA, 80D,80GG etc.
Apart from that your wife can get relief under section 87A, if net total income not increased from Rs. 3,50,000/-.