[pdftex] Adobe Battles Backward-Compatibility Woes

James Quirk jjq at galcit.caltech.edu
Wed Mar 15 18:01:26 CET 2006


On Wed, 15 Mar 2006, Hans Hagen wrote:
>> One way of handling "legacy documents" would be for Adobe to introduce
>> a system-hook whereby a PDF could be automatically filtered, before it is 
>> passed to a viewer. The idea being that the filter translates what
>> it finds into "compliant PDF," whatever that happens to be at
>> the time of viewing.
> Such filters have been around for a while: pdf/x cum suis compliance can be 
> tested in acrobat 6 and higher. Unless one messes around with pdfliterals in 
> uncontrolled ways, pdftex output is rather well pdf/x compliant. 
> A weak spot in pdf files can be tricky things with annotations and 
> javascripts and multi-media stuff; such (new) features have always been 
Annotations are the specific reason I moved to using a PDF filter,
or pre-procssor, back in 2001. At the time it was done as a 
means of passing arguments to a /Launch action, which could not,
and still cannot be done, under Linux.

The filter scans the PDF replacing the launch actions with ``shell 
launchers'' that are generated on-the-fly, and it is these launchers that 
then activate the annotation's commands with the appropriate arguments. 
This all happens transparently, but a savvy user, if they desire, can 
introduce their own layers of security to safeguard against trojan horses.
It also has the benfit of allowing the lauched command to unpack
and operate on objects from the document, say to extract the
source for the document, or to launch a movie file. Again, my
efforts in this direction were largely driven by the deficiences
of the Linux version of AR. And the hope is that as functionaility
appears, I can cut back on what my filter needs to do.

> unstable, subjected to subtle changes, etc. I normally tend to not supporting 
> things like that officially unless proven stable (enough) which often means 
> skipping at least one version (of pdf or the viewer)
I couldn't agree more. But given the usual delays in the release of AR 
for platforms other than MicroSoft, plus the inconsistencies that are 
present when the other releases finally arrive, it often feels like
a lost battle.


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