[pdftex] Fonts

[John Culleton]

On Sunday 30 March 2003 07:11 pm, Reinhard Kotucha wrote:
>
> The encryption stuff has been removed from pdfTeX but the question is
> whether the PDF format allows to set a flag that inhibits printing.
>
> Encryption is more or less useless, anyway.  Acrobat displays the PDF
> file in highest quality, but you need a password for printing.
>
> The same holds true for xpdf, but the difference is that xpdf provides
> it's source code.  A reasonable good C-programmer should be able to
> print anything that could be displayed on screen without loss of
> quality.
>
> Or does the PDF file contain the same information twice:
>    Once with limited quality for display on screen and
>    once in high quality (and encrypted) for printing?
>
> I doubt.  And the question is:
> Does the PDF spec allow to set a flag that says that printing is
> discouraged?  That would be a little bit useful, though not safe at all.

In answer to the last question, yes it does. It is called a copyright notice 
:-)

The quality of the screen display is limited by the screen dpi. So if one 
should
capture a page from the screen, edit out the borders, and print the results
then the resolution would be the equivalent of 72 or 75 dpi, not the 300
to 600 dpi expected for ordinary printing on a laser or inkjet printer.
OTOH if one hacks Xpdf as suggested above the file could be printed at its
expected resolution. 

Bottom line, there is no defense possible against a reasonably diligent thief.
Some discouragements I plan to use include:
1. An unhandy page size, to make printing the file wasteful. 
2. A copyright notice.
3. For e-books purchased from my site, an innocuous looking code that
in fact zeroes in on a particular copy and hence a particular customer.