Off-spec PDF support

No, Adobe does not make such information public. If we did, it would only further encourage such bad behaviour on the part of those creating PDF files.

Many problems, but not all, can in fact be found via the Acrobat Pro Preflight functions.

No, there is no way to know. You should start by considering carefully that Acrobat it NOT a validator, that is an entirely different task. It job is to accept valid files. Its job is NOT to reject bad files, though it will sometimes do so. Behaviour with non-conforming files is not defined by the standard.

In general, there will be two particular reasons why a specific non-conforming file may be accepted and produce some undefined result which matches some people's expectations:

- by accident; perhaps it does not check and the bad file happens to deliver what is looked for

- by design, perhaps to accomodate specific errors found to be made by PDF producers, including Adobe and third parties. These might be the results of bug reports, feature requests, internal QA decisions, or random decisions made without any discussion by a lone programmer.

I remember one case where Adobe reimplemented part of Acrobat, and had different checks. They rejected a large number of non-conforming files which were in common use, and from consideration for their customers Adobe modified to the code to specifically allow these non-conforming files to work as well as before. (From memory, the feature was allowing leading space in place of leading zero in some xref entries).

- I don't believe Adobe makes that information public.

- When you open a file using the SDK the same process happens if you open it manually.

- If they didn't implement something like that a large percentage of PDF files could not be opened at all, since many PDF generators do not adhere to the ISO standard 100%, so concessions have to be made.