A PAN card is a unique 10 character code that is assigned to all tax paying entities in India. If the two are not linked by the end of the day, your income tax returns will not be processed. Says a notification on the Income Tax E-filing website. The last date for PAN card-Aadhaar linking has already been extended once so the government is unlikely to give citizens more time once the deadline ends. Moreover, if the process to link PAN card with Aadhaar is not completed in time, the IT returns filed this year will become void, attracting a penalty of up to Rs. 5,000 and heavy interest can be levied in case of payable taxes. The Aadhaar PAN linking must be done irrespective of whether you provided the acknowledgement number for Aadhaar card, or quoted it in the tax returns form.