Open the Income Tax e-filing portal https://incometaxindiaefiling.gov.in/. Register on it (if not already done). Your PAN (Permanent Account Number) will be your User ID. Log in by entering User ID, Password and Date of Birth. A pop up window will open asking you to link your PAN with Aadhaar. If the pop up window does not open then go to ‘Profile Settings’ on the menu bar and click on ‘Link Aadhaar’. As per the PAN, the details like name, date of birth and gender will be mentioned there already. Verify your Aadhaar and PAN card details. If the details match, enter your Aadhaar number and click on the “Link Now” button. A pop-up message will inform you that your Aadhaar has been successfully linked with your PAN.