PDF/A is an ISO standard for archiving PDF files. It aims to preserve documents for the long-term by specifying a limited set of features to ensure validity over time and eliminating features that are not archival-friendly. PDF/A excludes features like audio, video, encryption and external links to ensure the file will remain renderable and accessible in the future. The standard comes in different versions, with PDF/A-1 focused on accessibility and PDF/A-2 extending it to allow additional features like transparency and embedded files while maintaining compatibility. Proper preservation requires more than just format conversion, including quality control, metadata, and ongoing monitoring to keep preservation formats valid over time.