Is it compulsory for a PAN card holder to file Income Tax?

It's not compulsory for a PAN holder to file income tax return if his/her income is below exemption limit i.e., Rs. 250000. However it's not mandatory but it is advisable to file income tax return even with no income or no taxable income as it has many advantages.
If you apply for any kind of loan either its car loan, home loan etc. then the lenders ask you for the income tax return of last three years. Filing income tax return strengthens your credit score and let lenders know that you have some income and you can be trusted. Same applies when you file for a Visa. Also when a company cut TDS on any amount and if your income lands in no taxable zone then you can claim refund.

The main criterion for filling IT return is that if an individual has taxable income of more than 2.5 lacs then he is supposed to fill a return and pay the tax or get the refund if some tax has been already imposed him through TDS route.

Those persons who have incomes around this boundary of 2.5 lacs, they are generally advised to fill the return so that if during some years it is more than that then consistency of filing returns will be there as IT departments ask for last year return if you submit the return for the first time.

If you hold PAN card it is not necessary to file to file income tax.
Let's understand what is PAN:
Permanent Account Number (PAN) is a code issued by the Department of Income Tax. It is a 10-digit number-and-alphabet combination and is unique to each individual. All taxpayers, a producer or manufacturer of excise-able goods, services must hold PAN.

Income tax is filed when your income falls under:

Income Tax Slab for Individual Tax Payers (Less Than 60 Years Old) for Fiscal Year (2018-19):
- Income up to Rs 2,50,000: No tax
- Income from Rs 2,50,000 – Rs 5,00,000: 5%
- Income from Rs 5,00,000 – 10,00,000 : 20%
- Income more than Rs 10,00,000: 30%
- Where total income exceeds Rs.50 lakh up to Rs.1 crore: 10% of income tax (Surcharge)
- Where the total income exceeds Rs.1 crore: 15% of income tax (Surcharge)

Income Tax Slab for Individual Tax Payers (60-79 Years Old) for Fiscal Year (2018-19):
- Income up to Rs. 3,00,000: No tax
- Income from Rs. 3,00,000 - Rs. 5,00,000: 5%
- Income from Rs. 5,00,000 - Rs. 10,00,000: 20%
- Income above Rs. 10,00,000: 30%

Income Tax Slab for Individual Tax Payers (80 Years Old or more) for Fiscal Year (2018-19):
- Income up to Rs. 5,00,000: No tax
- Income from Rs. 5,00,000 - Rs. 10,00,000: 20%
- Income above Rs. 10,00,000: 30%

Including:

- Where total income exceeds Rs.50 lakh up to Rs.1 crore: 10% of income tax (Surcharge)
- Where the total income exceeds Rs.1 crore: 15% of income tax (Surcharge)
- Education cess

Income Tax Rates for HUF/AOP/BOI/Any other Artificial Juridical Person for Fiscal Year (2018-19):
- Income up to Rs. 2,50,000: No tax
- Income from Rs. 2,00,000 - Rs. 5,00,000: 5%
- Income from Rs. 5,00,000 - Rs. 10,00,000: 20%
- Income above Rs. 10,00,000: 30%

- Where total income exceeds Rs.50 lakh up to Rs.1 crore: 10% of income tax (Surcharge)
- Where the total income exceeds Rs.1 crore: 15% of income tax (Surcharge)
- Education cess.

Income Tax Rates for Partnership for Fiscal Year (2018-19):
- 30%
- 12% of tax where total income exceeds Rs. 1 crore (surcharge).
- Education cess.

For more details I would recommend you to visit website of Indian Income Tax Department and Central Board for Direct Taxes (CBDT).

No, it is not compulsory for all pan card holders to file income tax. You are required to file income tax return, only if your yearly income is taxable. Pan card is mandatory for opening a bank account in Indian and even all college students own a pan card. I am sure that they are not filing income tax return as they have no income.