Regular PDFs depend on external fonts, colors, and JavaScript that may not exist in 20 years. PDF/A solves this.
What PDF/A Does Differently
All fonts embedded (no external dependencies). No JavaScript or executable code. Color profiles embedded. Metadata in XMP format. Encryption prohibited (ensures future readability).
Who Needs PDF/A
Government agencies, legal firms, healthcare (medical records), financial institutions, and anyone who needs documents to be readable decades from now.