There are often times when you will want to take an existing
PostScript document and manipulate it in some way. For example, you
may be publishing a book, and you want to print the pages with wide
margins for proofing notes (but you don't want to modify the book's
layout). Maybe you are printing out some 100-page manual, and you want
to avoid using most of a rain forest to print it. Maybe you want to
print out some document with the word "Draft" stamped
beneath the pages. All of these things can be done in
PostScript by a postprocessor (that is, a program which manipulates an
existing PostScript file). Moreover, these are all things which may be
difficult to manage in the program you used to generate the files.
In this section, I'll show you the basic PostScript code to do each of
these jobs and how to use EPS comments to find the right places to
insert the additional PostScript.
You are welcome to use these programs as you will.
Bear in mind, however, that there are professionally written programs
that do these jobs and more. I strongly suggest that you look into
buying such a program rather than writing your own. Generally, they
have already solved most of the problems. Also, these packages usually
come with tools you did not even knew were possible. These examples,
therefore, are more to give you a taste of what is possible and how to
do it, in case you want to roll your own post-processing utility.