[gdal-dev] Re: Can PDF measuring be activated

[George Demmy]

On Fri, Mar 2, 2012 at 8:37 PM, Even Rouault
<even.rouault at mines-paris.org> wrote:
> Le vendredi 02 mars 2012 12:53:39, Jukka Rahkonen a écrit :
>> Even Rouault <even.rouault <at> mines-paris.org> writes:
>> > Le jeudi 01 mars 2012 22:19:34, Jukka Rahkonen a écrit :
>> > > Hi,
>> > >
>> > > The native measurement tool of Acrobat Reader stays greyed with the ISO
>> > > style georeferenced PDFs. From Abobe forum I found this:
>> > >
>> > > "Re: Measure tool disabled
>> >
>> > Ah, interesting. I was also wondering why I add only access to
>> > coordinates display.
>>
>> .....
>>
>> > At the very least, a sample that has
>> > gone through the enabling system in Acrobat would make it easier to know
>> > if it is feasable or not.
>>
>> http://latuviitta.org/documents/GDAL_ISO+OGC_3067_enabled.pdf
>
> Ok, looking at it confirms my initial feeling. I believe that it is not
> possible, due to the use of cryptography mechanism to protect the associated
> permission.
>
> Well, it might be possible if you have access the private signing key of
> Adobe. But this is not an encouragement to anyone to try to access to it...
> Make sure you know the Law before.
>
> Or it is perhaps doable if you have a proper X.509 certificate, use it when
> signing the doc and register it in Adobe Reader as a trusted certificate.
>
> Well, it is interesting to see that even if the PDF spec is open, such DRM
> mechanism can make it use similar as to if it was closed.

The following doesn't have much to do with GDAL dev directly, but
maybe it will be useful in the support of PDF hacking...

Here's the deal with Adobe's measurement tools. They are built on top
of their PDF annotation tools which modify the PDF document. By
default, PDF is read-only in Reader. Since the measurements are tied
to annotations which require modification of the PDF, you can't do it
by default. However, Acrobat Pro can embed permissions in the PDF file
which unlock the annotation/measurement functionality in Reader. The
PDF spec is open and nothing is hidden per se (content can be
encrypted, but that's something different) -- the issue here is DRM
controlling functionality in software. It's confusing if you don't
know about it...

HTH and cheers!

George Demmy