| Why won't my
PDF print properly?
Adobe has convinced computer users that PDFs are universally
portable. However, what you see in a PDF is how it will look when
This is especially true with respect to printing on high-speed
Viewing a PDF is not the same as viewing a printed proof of your book.
PDF stands for "portable document format." It was Adobe's idea
for using their postscript printer language to make document
files that would be independent of computer, operating system and also
independent of the application that created the document in the first
place. The idea is that Word users can share PDF files with WordPerfect
users. It is also that a PDF
created on a Mac will look the same if was viewed on a PC.
PDF is a way of packaging postscript to make it more easily
viewable. In recent years,
the PDF specification has been expanded to include all kinds of visual
and multimedia elements. In addition, the complexity of graphical
elements allowed within the PDF specification has grown.
Some document creation programs,
particularly sophisticated image editing programs like Photoshop and
publishing programs like InDesign, are capable of making highly complex
PDF files that have multiple overlapping image and font elements. These
elements can have varying amounts of "transparency," allowing partial
through them to reveal overlapped elements below. Eventually all of the
elements must be
flattened into a bit map image that is printed. The bit map is made up
of a two dimensional array of pixels, one per spot. Each pixel has a
color that depends on the order and transparencies of the overlapping
elements at that location in the original image.
For complex PDFs, the elements in different layers of the
image are "put down" on the virtual page in sequence. In
the PDF viewer (like Adobe's Reader) the image is assembled by going
back over the page, again and again, to add layer upon layer to the
doing that assembly, the resulting image that displays on your screen
is a simple bit map.
Again, each pixel of that assembled image has one set of color
codes. At this point the viewed image can be
printed by reading back all those pixels and printing them pixel by
pixel. This is a so-called "rasterized image."
When you print a PDF from a desktop computer the image is
usually assembled in the viewer and then printed as a bitmap. When a
PDF is printed in a commercial setting there is no viewer creating the
bitmap. Instead there is "RIP" software.
High-speed printers do all of the creation of a bit-mapped
print image in software before sending the data to the printer. The
software that does this is called a "RIP." RIP stands for "raster image
processing." For a high speed printer, The RIP software cannot afford
the time to do complex repainting of a virtual image until a page is
created and it can move on to the next page. Commercial RIP software assumes that the PDF is not complex.
The latest bells and whistles of PDF specification are not included in
part because it is expensive to keep revising and in part because it
would slow down the processing.
This is a well-know problem with PDFs
This problem is well-known,
if not exactly well-publicized. The commercial print industry
has be dealing with PDF incompatibilities for years. They finally
decided that it was necessary to create a subset of the PDF
specification that would have compatibility with commercial RIP
software. This grew into several sets of specifications and updated
specifications. You can learn about these by googling the Internet for
terms like PDF/X, PDF/X-1, PDF/X-3 and so on. These specifications are
limited subsets of the full PDF specification. Applications that can
create PDFs in these subset specifications have a better chance at
easily making documents that print well on commercial printers.
How does all this relate to
fonts and font embedding? Adobe's PDF specification allows a
large set of "built-in" fonts to be used without having the fonts
embedded into the PDF. The commercial RIP software has no such set of
built-in fonts. All fonts must be embedded in your PDF for it to print
Unfortunately, the process of font embedding is also somewhat complicated. There are different ways to embed fonts and not all of these ways are equally supported by commercial RIP software. In addition, some elements in the font embedding process can be non-standard and still allow the PDF to view reasonably but not to print properly. There are probably many ways this happens. The fundamental reality is that some versions of the widely used "ghostscript" program produce PDFs that are poorly supported by commercial RIP software.