PDF/A is an archiving standard that was published in 2005 by ISO. PDF/A-1 was based on the original Adobe PDF 1.4 version. This version set the standard for ensuring that PDF content could always be visually reproduced regardless of future changes to viewing and printing technology.
PDF/A-2 was released by ISO in July 2011. PDF/A-1 files are compliant archive documents and do not need to be converted to the new standard. PDF/A-2 does not replace the PDF/A-1 standard.
So, what is the difference between these two standards you might ask.
PDF/A-1 is based on PDF version 1.4 (based on Adobe PDF specifications).
PDF/A-2 is based on the ISO standard 32000-1 and takes advantage of features that came after the Adobe PDF 1.4 specification.
What is new in PDF/A-2:
- JPEG2000 compression (benefits for scanned color documents)
- Embedded PDF/A files via collections/portfolios
- Optional content (layers): useful for mapping or engineering drawings or documents with multiple languages (implement different content on different layers)
- Unicode support (PDF/A-2U)
- Object level XMP metadata (new requirements for custom metadata)
- Comments and annotations (defined list of acceptable and prohibited annotation and comment types for PDF/A-2)
- Digital signature rules defined.
Read more about PDF Standards here.