Legal document plays an important role in judicial, administrative and business sectors but is vulnerable to tampering, forgery and unauthorized replication. These vulnerabilities undermine the credibility of transactions and reduce public trust in organizations. Conventional paper-based techniques and centralized storages are generally unable to guarantee authenticity, long-term integrity, and secure traceability. As the need for clear and scalable verification increases, systems are required that give cryptographic guarantees without the need for manual intervention. This work introduces a cloud-native, tamper-evidence 2 counter based encryption to address the presented and many other perspectives auth-system using only serverless AWS integrations. The architecture utilizes Amazon S3 for secure storage, AWS Lambda as a sever-automated hashing, Amazon QLDB for immutable ledgering, and AWS Amplify for a user-facing interface. The system achieves 100% accuracy evaluating tasks of detecting duplicate documents and it also offers end-to-end evaluation in about 1.2 s. By combining blockchain-inspired immutability with managed cloud infrastructure, the proposed solution offers a practical, low-cost approach to modernizing legal document authentication with strong guarantees of integrity and verifiability.