PDF has emerged as one of the predominant formats for creating, capturing, storing, and delivering electronic documents. As it is increasingly applied to content deserving or requiring long-term retention, questions arise as to what technical mechanisms and best practices can ensure effective preservation. Long-term preservation entails not merely maintaining the fixity of the byte stream, but also ensuring continuing access to, and interpretation of, the full information content of archived PDF documents. PDF supports many sophisticated features that tend to subvert efforts towards effective preservation. To address these concerns the International Organization for Standardization (ISO) has established a joint working group to develop a standard to specify how to use PDF for long-term preservation of electronic documents. ISO 19005-1, known familiarly as PDF/A, defines a constrained subset of the file format and a set of functional requirements for PDF/A readers. This paper provides a snapshot of the evolving PDF/A standard and addresses its potential impact for digital preservation.