Introduction - PDF Explained - page 11

Document Archiving
Through PDF/A, PDF is the ideal format for long-term archiving, combining accurate
representations of scanned and electronic content, together with Unicode language
support, and compression mechanisms for all sorts of data including the important
CCITT Fax and JBIG2 methods for monochrome images. Being an ISO standard (and
one which is near-ubiquitous) guarantees that these documents can be read long into
the future.
PDF can be used for Optical Character Recognition (OCR), allowing searchable text
to be created from the original, the exact visual representation being retained alongside
the recognized text.
As a File Format
PDF is not, at first sight, suitable for use as an editable vector graphics format. For
example, a circle won't remain editable as a circle, since it will have been converted to
a number of curves (there is no circle element in PDF).
However, if appropriate use is made of its extensibility to store auxiliary data, it makes
a good solution. Adobe Illustrator, for example, now uses an extended form of PDF as
its file format. The file can be viewed in any PDF viewer but Illustrator can make use
of the extended data when it is loaded back into the program.
Useful Free Software
In this topic, we use various pieces of software to help us with examples. Luckily,
everything you need is freely available. You'll need a PDF viewer:
• Acrobat Reader is Adobe's own PDF viewer. It supports all versions and features
of PDF and comes with a browser plug-in on most platforms. It's available for
Microsoft Windows, Mac OS X, Linux, Solaris, and Android.
• Preview is the pre-installed PDF viewer and browser plug-in for PDF documents
on Mac OS X. It's highly capable, and very fast, but doesn't support everything
that Acrobat Reader does. Many people stick with Preview as the default applica-
tion for PDF files, but install Acrobat Reader as well.
• Xpdf is an open source PDF viewer for Unix. It supports a reasonable subset of PDF.
• gv is a PostScript and PDF viewer frontend for GhostScript (see below). It can
render the textual and graphical content of almost all documents. However, it lacks
most of the interactive features of other PDF viewers.