There are vast differences between software that perform the
same functions, and although encryption is generally used to preserve
the integrity of those functions, in some cases the encryption
may not be adequate and in others it may not exist beyond masking
the file's properties*:
Adobe Acrobat is a well know PDF editor/creator which provides options
for locking a PDF to prevent changes to its contents. Some other
PDF editors also provide this option which usually required the
use of a password for an author to make any changes.
As above, printing of a PDF can be prevented by locking with a password.
This may prevent a user from using print controls within a reader
but may not prevent them from using other print commands. Proper
print control needs to control all devices connected to a computer
including printer drivers (plugins) such as those used to convert
documents to PDF.
Password protection is probably the most commonly employed method
of restricting unauthorized access to a PDF documents contents.
When a password is applied an user wishing to open that PDF needs
to type in the correct password before the document will open. However
anyone wanting to distribute your document only needs to include
the password with it. As already mentioned, the security of passwords
stored in PDF are only as good as the encryption used to hide them**.
Another popular method of protecting PDF is by applying an expiry
date after which the PDF cannot be opened. This is most useful for
making information available for a limited time and limiting sharing
to a set window of opportunity. For example an author can send a
document to someone and after say 5 days that PDF will no longer
be accessible... to anyone. Unfortunately most readers depend on
local computer time, which is the time displayed on the user's computer,
and such expiration can be thwarted by simply turning back the computer
CopySafe PDF solves this problem by offering the choice of using
local time or online time server checks.
Access control of a PDF is basically about limiting just who can
open the document. Often referred to as digital rights management
but more aptly known as "document rights management",
DRM requires a means of assigning authority for an individual user
to open the document. Early forms of DRM for documents used certificates
that could be stored in a user's computer registry and checked when
using a proprietary reader. DRM certificates are most useful and
not dependent on an Internet connection, but even though they may
use extremely secure encryptions, being stored on the user's computer
they can still be exploited and shared. A more secure method was
developed for ArtistScope
DRM which utilizes an online service to validate each user according
to their unique computer signature.
Some PDF protection software may provide options for allowing or
disabling print, and as we have already mentioned above, that restriction
may only be hiding the print button, but not preventing print by
other methods such as using a command line. But only few of those
applications can effectively control the number of prints allowed.
Some may effectively control the number of visits to a printer,
in which case on any occasion the user can print 1,000 or more copies,
but there is only one application that can effectively control
how many prints are made.
As with controlling the number prints, with DRM you can also limit
the number of times a PDF can be opened per user. For example an
author can set a limit of 5 views of a document after which it cannot
be accessed. From a teacher's point of view, if they haven't absorbed
the information by then, then their time has run out. Or a document
can be set for one view only, after which it becomes inaccessible
to that user. Again, ArtistScope
DRM may be the only program that can cater for this feature
and remain unexploitable.
Most of the methods described on this page are about protecting
PDF, but so far have only been concerned with preventing access
to the document's contents. But what can be done about protecting
the document's contents from copy while on display? Well when
considering all of the methods available today for making a copy
by save, Printscreen and all of the screen capture software available
today the task can seem daunting. There are some applications that
do prevent Printscreen but there is only one that prevents all copy
CopySafe PDF Protector provides the most secure document protection
and was specially designed for integration with
Most people think that because a file can be sent by email that
it can been exploited, and in most cases this will be true because
nothing will prevent a user from sending any file by email. But
there is something that can be done to that file to make it useless
to any recipients who are not authorized to read it. For example
if DRM is applied to a PDF document then it doesn't make any difference
how many users send thousands of copies to any number of recipients,
because only those recipients who have the author's permission
and the correct reader will be bale to open the document. For
more information on how this works with a practical demonstration
for evaluation, try creating a demo account with a DRM
* To prevent documents from being opened in generic readers sometimes the file's header is mangled instead of properly encrypting the document. Many programs claiming to use "strong encryption" are actually not encrypted at all.
** There are many programs available today for the extraction of passwords from PDF. Unless the reader and the document are designed from end to end to preserve the integrity of encryption, they can be exploited. Readers such as Adobe Reader are designed to be user-friendly and their source code is available to too many programmers to remain secure.