Ghostscript's PDF/A conversion re-embeds non-embedded CID (CJK) fonts by
substituting a system font, which corrupts the character-to-Unicode
mapping and silently destroys an existing text layer -- commonly the OCR
layer Adobe Acrobat adds to scanned CJK documents.
Detect non-embedded CID/Type0 fonts before conversion: with
--output-type auto (the default) downgrade to a regular PDF and preserve
the text layer; with an explicit --output-type pdfa* stop with an error
rather than emit corrupted output. Simple non-embedded fonts (e.g. Latin)
are left alone -- Ghostscript substitutes them without corrupting the
text, and they are far too common to treat as conversion blockers.
Use --output-type pdf to keep the existing text layer, or --force-ocr to
rebuild it with embedded fonts.
Acrobat insists that PDF/A-1b should not have object streams.
Other programs like veraPDF disagree with this restriction, but
we can accommodate Acrobat so we will.
Also add more tests around this.
James R. Barlow