PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for the digital preservation of electronic documents.

PDF/A differs from PDF by omitting features ill-suited to long-term archiving, such as font linking (as opposed to font embedding). (Similarly, the PDF/X file format is specially adapted to digital printing and graphic arts.)

The ISO requirements for PDF/A file viewers include color management guidelines, support for embedded fonts, and a user interface for reading embedded annotations.

Read more about PDF/A:  Standards, Background, Description, Identification, PDF/A Viewer Mode, Drawbacks, See Also