Many business processes require documents and transactions with trusted signatures. This has been a key issue that blocks enterprises from transforming paper-based business processes into e-business processes. Digital signature and PKI technology make it possible that documents and transactions with the need for signatures can be electronically signed and processed. We describe in this paper the design and implementation of an enterprise portal for secure document management. The portal is a Web-based management system that can be used to, at the enterprise level, streamline document-based business and personal transactions, and securely maintain e-documents in the centralized database. To automate and secure the process of document-based transactions, e.g., filing travel expense reports, the system integrated digital signature and PKI technology for digitally signing and managing documents and forms. Compared to other systems, it is open to various types of user authentication mechanisms, it supports the signing and verification of most document formats, and it provides a Web service endpoint for application integration, aggregation, and automation.