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QUESTION: What's the difference between PostScript and PDF?
ANSWER: In a very basic sense, PostScript
and PDF are similar - each is a file format that describes text
and graphics.
However, there are some important differences between PostScript
and PDF.
For many people, the most important difference between PostScript
and PDF is that it's easy for most computer users to view
PDF files on the screen, but it's difficult or impossible for
most computer users to view PostScript files on the screen.
That's because it's easy to obtain good-quality PDF-viewing
software (the Adobe Reader software) free of charge,
but it is not as easy to obtain PostScript-viewing software.
(If you don't know how to view PDF files on the screen,
click here.)
Another difference between PostScript and PDF is that PostScript
is a programming language but PDF is not. This
difference, while important, is probably meaningful only to
you "techies" (i.e., those of you who write computer
programs). PostScript is a programming language because it has
things called "conditional constructs," "looping
constructs," and other things associated with programming
languages. PDF does not have these things.
Also — in general — a PDF file that describes a particular document
is smaller than a PostScript file that describes the same
document. This is important, because smaller files can be
handled more efficiently than larger ones (it takes less time to send
smaller files across a network; smaller files take up less space
on your computer's disk).
You might have noticed that — with the sample PostScript file
and sample PDF file shown at www.citationsoftware.com/faqPostScript.htm
and www.citationsoftware.com/faqPDF.htm,
respectively, the opposite is true: the PostScript file is smaller
than the PDF file. However, for real-life files, it's usually not
this way.
The structure of PDF files is much more predictable than the
structure of PostScript files. This is important in situations where
software needs to modify a document or extract information from a
document.
And PDF can do lots of things that PostScript can't do. PDF files
can be viewed on the Web (with the proper software), whereas
PostScript files normally cannot. A PDF file can contain links
to locations within the same PDF file, within other PDF files,
or on the Web; a PostScript file normally does not contain links.
A PDF file can function as a data-entry form but a PostScript
file cannot. There are lots of other differences, too.
For these reasons and more, PDF has become a replacement for
PostScript in many situations.
For additional information about PostScript and PDF, visit
www.adobe.com.
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