Re: PDF is blocked for printing, etc. OK for acroread (it behaves as expected), but KPDF allows me to print it, even if it is protected! Why?

Vincent Danjean wrote:
On 19/04/2010 17:32, Merciadri Luca wrote:


If you have free software (ie software you have the sources and are able
to recompile) and if you can get the information on the screen, then it is
only a matter of programmation to be able to have it on printer. So,
free software readers that forbid printing can be (more or less) easily
circumvented (and the patch to do this will be done and available on
internet). So why would the authors of such readers want to program this
at first time.

If you want to avoid printing, you need to fully control the whole chain
(ie TPA, ...) AND the terminals (ie, if you can show it on screen, some
classic 'print-screen-to-file' and graphical software can be used to
print the document, or even camera and image post-processing).

For now, the only domain where such restrictions works partially are
HD-DVD (and its possible it is already broken). This is possible because
it is expensive to acquire good quality video data (ie recording what
is diffused by a secure HD player on screen by a camera will have
no really good quality). This would not work for audio data (at least,
until the decoder is not embedded into brain ;-) ) because it would
be easy to reacquire good quality data from a line-out.

Thanks for this great explanation.
So, what would be the use case to allow a someone to read the information
but not print it ? In any case, printing it would be more or less convenient
but it will always be possible if it is displayed on screen (even
with Acrobat Reader)

My reason is quite complicated, and is really justified. Briefly, one
person that I know needs to have some report I wrote, but this person
should not be able neither to print it nor to extract content from it,
for a simple reason: this person could transmit a part (or the whole)
[of the] document to a third party, and this third party should not
receive the report from the person who could send it to him (the third
party), but the third party wants the other fellow (actually not a
fellow to me) to receive the report.

I know that it is _always_ possible (with some determination) to extract
content, by some way, of a PDF (even if screenshots were to never work,
you can still use a camera). Principally, the most important aspects of
such security features are that they are tricky (for some users only, I
agree) to unlock, and that they are consequently repulsive at prima facie.

--
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
I use PGP. If there is an incompatibility problem with your mail
client, please contact me.




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