Taxpayers face a critical December 31 deadline for several financial obligations. This includes linking PAN cards with Aadhaar to avoid penalties and an inoperative PAN, filing belated Income Tax Returns (ITR) for FY 2024-25 with potential late fees and loss of benefits, and submitting annual GST returns for businesses. Missing these deadlines can result in monetary penalties, interest on unpaid taxes, and increased scrutiny from tax authorities.