PDF/A levels backward compatibility?

[Marek Melichar]

Regards,


we are trying to create veraPDF validation profile for PDF/A repository.


Contrary to our expectation some PDF/A pass as valid representations of PDF/A-1a and do not pass PDF/A-2u validation (using VeraPDF version 1.0)

We meet the error related to CID fonts - https://github.com/veraPDF/veraPDF-validation-profiles/wiki/PDFA-Parts-2-and-3-rules#rule-62114-4

It seems that levels 2u or 3a are in fact stricter then 1a level...

best 

Marek

[Michael Kjörling]

On 16 Jan 2017 01:15 -0800, from marek.m...@gmail.com (Marek Melichar):

> It seems that levels 2u or 3a are in fact stricter then 1a level...

Even Wikipedia[1] states that:

> PDF/A-1 files will not necessarily conform to PDF/A-2, and PDF/A-2
> compliant files will not necessarily conform to PDF/A-1.

I haven't looked through the actual standards (the relevant citation
is an ISO standard) but given that PDF/A-2 is intended to address
features added by later versions of the PDF file format than were
available at the time PDF/A-1 was standardized, I suppose it makes
sense that things that are valid in one might not be valid in the
other.

[1]: https://en.wikipedia.org/wiki/PDF/A#Conformance_levels_and_versions

--
Michael Kjörling • https://michael.kjorling.se • mic...@kjorling.se
“People who think they know everything really annoy
those of us who know we don’t.” (Bjarne Stroustrup)

[Boris Doubrov]

On Monday, January 16, 2017 at 7:13:14 PM UTC+3, Michael Kjörling wrote:

On 16 Jan 2017 01:15 -0800, from marek.m...@gmail.com (Marek Melichar):
> It seems that levels 2u or 3a are in fact stricter then 1a level...

Even Wikipedia[1] states that:

> PDF/A-1 files will not necessarily conform to PDF/A-2, and PDF/A-2
> compliant files will not necessarily conform to PDF/A-1.

Indeed, there are several differences in graphics requirements between PDF/A-1 and PDF/A-2 (PDF/A-3 is identical to PDF/A-2 in this matter). For example, the requirements around CID font subsetting are a bit different.

In more detail, CID font subsets embedded into PDF may include a special entry /CIDSet  that identifies which glyphs arepresent in this subset. For PDF/A-1this entry is mandatory,while for PDF/A-2(3) it is optional, but if present it shall correctly identify all glyphs in the subset.