Taxpayer is required to login on e-Filing portal using his registered username and password. After login, he will get the “link Aadhaar” option under his ‘Profile Settings’.
Aadhaar number will be linked with PAN if name and date of birth of taxpayer is identical to Aadhaar and PAN.
Source: Income Tax India’s Official Website
Aadhar lists name as “last name+first name” whereas PAN lists name as “first name+last name”, obviously they won’t match. How such a comparison was made by such greats like Nandan Nilekani is only known to them. They created such a stupid system.