Linking PAN to Aadhaar is now compulsory. Here's how to do it
If you have not linked your Aadhaar with your PAN on the income tax portal yet, you should not delay it. As per latest circular from income tax (I-T) department, it is now mandatory to provide Aadhaar and permanent account number (PAN) details while filing tax returns. The rule which will be applicable from July 1, 2017 is aimed at tax evaders who hold multiple PAN cards to escape paying tax. Therefore, after linking both the Aadhaar and PAN, the government hopes to keep tabs on the taxable transactions of a particular individual or entity, whose identity and address will be verified by his Aadhaar card By linking the two, entities will no longer have to submit their Income Tax acknowledgement to the I-T department, thus saving tax payers a lot of trouble. When linking, make sure that name, date of birth and gender displayed on the income tax website matches with the detail on your Aadhaar Card. Here’s how to do it: 
The first step towards linking Aadhaar with PAN is to register on Income tax e-filing portal.