Guidelines
for Generating PDF Files
We offer these guidelines to assist authors in the
preparation of the PDF papers for online submission. However, because of the
multitude of computer platforms in existence today and the rapidly evolving
software, we do not attempt to provide detailed instructions that cover all
possible computer/software configurations.
Why PDF?
We require that all papers be converted to Portable Document
Format (PDF) before submission. Why?
-
PDF files
allow users on different platforms (e.g., Windows, Mac and UNIX) to view files
as originally intended by the author, if created properly (see
PDF Creation Tips).
-
PDF files
can be read by almost anyone with a computer, using free software, such as
Acrobat Reader, or
GSview (which is a Windows previewer for
Ghostscript).
-
Once the
proper software is installed, it is very easy to create a PDF file.
-
Other file
types are not really standards. For instance, there are many flavors of
PostScript and many applications that produce PostScript output do so
imperfectly.
How to
Convert to PDF?
The word processor software used to prepare the paper in
electronic form produces a file in its native format, e.g., *.doc for MS Word,
*.dvi for LaTeX. This file should be converted to PDF (*.pdf ), which is usually
a two-step process: the file is firest converted to PostScript (*.ps), then from
PostScript to PDF. In Windows, the first step may be accomplished by simply
selecting a PostScript printer in the Print Menu and printing to a file (this
assumes that the PostScript printer driver has been installed). When LaTeX is
used, the conversion is accomplished by DVI-to-PS converters, such as dvips
(use the command line options dvips –Pamz –Pcmz <<dvi filename>>). The
second step, from PS to PDF, may be accomplished using Acrobat Distiller (which
is included with the
Adobe Acrobat ) or the freely available
GSview/Ghostscript. Alternatively, one can use the free, web-based
PS2PDF converter. With Acrobat Distiller, it is also possible to convert
files to PDF directly from within the authoring application program (e.g., MS
Word).
The Font
Lore
The authors should always use scalable outline fonts, rather
than bitmapped fonts. In outline fonts the letter shapes are described by means
of lines, arcs, and curves.
This representation is resolution-independent, because the
outlines can be scaled to an arbitrary size. Hence, if you make an outline
character ten times as big, it is just as accurate as if it were ten times as
small.
Two common examples of outline fonts are Adobe PostScript
(Type 1) fonts and MS/Apple True Type fonts. Each character in a PostScript font
is described by a small PostScript program specifying character outlines. To
realize the characters on an output device, the PostScript interpreter
rasterizes the outlines dynamically and transforms them into bitmap image,
taking into account the resolution of the output device. The rendering machine
for True Type fonts is built into the operating system (Windows or Mac). In this
context, we should also mention Type 42 fonts, which consist of a PostScript
language "wrapper" around a True Type font. A Type 42 font is usually generated
by a printer driver to download True Type fonts to a PostScript printer that
includes a True Type rasterizer.
A PDF-producing program can deal with a font in one of three
ways: it can
-
take the
entire font and embed it in the file; or
-
make a
subset font of just those characters used in the document and embed that
subset; or
-
only embed
some summary details about the font (such as its name, type, size, etc.) and
rely on the display program to either find the named font on the local system
or --- if one is not available --- substitute some similar local font.
Embedding fonts essentially means to include in the PDF file
the information necessary to faithfully recreate the characters used in that
file. If fonts are not embedded and do not reside on the computer where the PDF
file is viewed, another font available to the PDF reader will be substituted.
The substitute font may have different characteristics or characters (e.g., a
bracket in a mathematical equation can be replaced by a column of letters),
hence the file may not look like the one created on the original system.
Font subsetting is a process of embedding only those
characters that are used in the file, rather than embedding the entire character
set of a font. This process is controlled by the subsetting threshold (also
called the maximum subset percentage). If the latter is set to X%, this means
that if less than X% of the characters in a given font are used in the document,
this font is subsetted; otherwise, the entire character set of the font is
embedded. Hence, X=100 means that even if 99% of each of the embedded fonts'
characters are used in the document, only those characters actually used will be
included. Font subsetting is a way to satisfy the licensing conditions if
proprietary fonts are used (because the font will not be entirely embedded); it
also has the desirable effect of making the document smaller. When the PDF
converter embeds a subset of a font in a PDF file, it assigns a new, unique name
to the font. Because the new names of the subsetted fonts in the PDF file will
never match a font on a host system, the viewer will always view and print using
your version of the fonts. Raster Image Processors (RIPs) will always use a
subsetted font, even if the full font is already available on the RIP. This way
text reflows caused by differences between fonts can be avoided. Therefore, font
subsetting makes the document extremely reliable.
We ask the authors to always embed all fonts and to subset
them at a threshold of 100%. To ensure the desired results, the authors should
check the settings of the conversion program and adjust them accordingly. For
example, in Acrobat Distiller the box "Embed All Fonts" should be checked in the
"Job Options" panel. Also, delete all font names appearing in the "Never Embed"
window. Acrobat Distiller by default does not subset the font if more than 35%
of the characters are used.
Hence, you should check the box "Subset fonts below" in the
"Job Options" panel and set the maximum subset percentage to 100% to ensure that
Distiller always subsets unless every character of the font is used.
Please use in your document standard Type 1 or True Type
fonts, such as Times Roman, Times New Roman, Helvetica or Arial. In order to
find out what fonts are included in your PDF file, view it in Acrobat Reader and
click on File>Document Properties>Fonts. This will show the list of fonts and
their type (Type 1, True Type, Type 3, etc.) and will identify if any of the
original fonts are substituted with others by Acrobat (on your system).
Including
Graphics/Images
All images must be embedded in your document. The type of
graphics you include will affect the quality and size of your paper. In general,
the use of vector graphics such as those produced by most presentation and
drawing packages can be used without concern and is encouraged.
The use of bitmapped images such as those produced when a
photograph is scanned requires significant storage space and must be used with
care. Bitmap graphics store an image as a series of numbers that represent the
color of each dot in the image. Increasing the size, resolution (dots per inch),
or number of colors in an image will dramatically increase the size of the
image. If your paper contains many large images they will be down-sampled to
reduce their size during the conversion process.
However the automated process used will not always produce
the best image, and you are encouraged to perform this yourself on an image by
image basis.
Do not use custom halftones and pattern fills. Instead use
solid-color or gray-scale fills to produce a more readable document on-screen
that will also load and print significantly faster. Also, do not select the
"Smooth Graphics" option offered in some applications software. This option
often produces extremely large files that will take a long time to display and
print.
Suggestions for improving the quality bitmap graphics
include:
-
In
general, bitmapped images should be limited to no more than 256 (8 bit) color/gray
scale, 150 dots per inch, and should be kept as small as possible.
-
Reduce the
number of display colors before making screen shots. The majority of computer
applications use less than 16 colors for their menus, dialogs etc.
-
Select
higher resolutions only for images that a reader will magnify. Image
resolution of bitmapped images does not increase when readers zoom in on an
image.
Creating a
PDF file using GSview/Ghostscript for Windows
Once
GSview/Ghostscript and a PostScript driver are installed on your computer,
it is easy to create PDF files from your documents. This is a two-step process:
first, a PostScript file is created; next, the PostScript file is "distilled" to
PDF file.
Making a
PostScript file
-
Open the
document in its native application (e.g., MS Word).
-
Print the
document using the usual command to call up the Print dialog.
-
From the
Print dialog select Adobe PostScript Printer (or whatever PostScript printer
you have installed).
-
Check the
box "Print to file".
-
Save the
file as *.ps file, not the default *.prn file! (Change the file type to "All
Files", then type the file name including the ".ps" suffix.)
You should now have a PostScript version (*.ps) of your
original document. Browse to that file from Explorer and double-click on it to
open it in GSview. Another way to open the file is to start GSview from the
Start menu (Start>Programs>GSView). From the GSview menu go to File>Open and
browse to your PostScript file.
Distilling the PostScript file to PDF
-
Open the
PostScript file (*.ps) in GSview, as explained above.
-
From the
GSview menu click on File>Convert.
-
From the
Device menu select pdfwrite and set the Resolution to 720.
-
Click the
Properties button and make sure that: EmbedAllFonts and SubsetFonts are set to
true, set PDFSETTINGS to /prepress and MaxSubsetPct to 100.
-
Click the
OK button. An "Output Filename" dialog will pop up.
-
Browse to
wherever you want your new PDF file to be located.
-
Give the
file a name, using a ".pdf" suffix.
-
Click the
Save button. In a few seconds (or a few minutes, depending on the size of the
file and the speed of your computer) you will have a PDF version of your
document. While GSview is working you will see an icon on the Windows taskbar
that gives an indication of progress expressed as a percentage. Be patient:
wait until the icon disappears.
Now you can browse in Explorer to the directory where you
told GSview to create the file and, if you have
Acrobat Reader installed on your system, you will be able to open the file
by double-clicking. NOTE: If you want to open the PDF file in GSview, then you
must start GSview and browse to your file from the File Open dialog.
It is also possible to associate the ".pdf" extension with
GSview, so that double-clicking a PDF file will open it in GSview. (Select
Options >Advanced Configure from the GSview menu and check the box "Associate .pdf
files with GSview".)
Creating a
PDF file using Acrobat Distiller for Windows
Before you create the document, specify Acrobat Distiller as
the default printer. Once the document is created, do as follows:
-
Open the
document in its native application (e.g., MS Word).
-
Click on
File>Print, which brings up the Print menu.
-
From the
Printer window, select Acrobat Distiller.
-
Leaving
the "Print to file" box unchecked, and choosing the "Press-Ready" option,
click the OK button.
The PDF file will have the same name as the PostScript file,
plus the extension ".pdf". Now you can browse to that file and open it in
Acrobat Reader by double-clicking.
Installing
a PostScript printer driver
You don't need to have a PostSript printer connected to your
computer in order to install a driver for one. The drivers are printer-specific
and they depend on the manufacturer and the printer model. In principle, any
PostScript printer driver can be selected (if the name ends with "PS", this
indicates that the printer has PostScript support). However, not all PostScript
printer drivers generate identical output. If you are a Windows or Mac user, it
is best to download and install an Adobe PostScript printer driver from one of
these sites:
Windows drivers,
Mac drivers.
Creating
PDF from LaTeX source
LaTeX systems have traditionally depended on the use of fixed
resolution bitmap fonts and DVI-to-PostScript converters default to such fonts.
Bitmap fonts are embedded in PostScript output as Type 3 fonts. Since these
fonts are generated at a given resolution and for a given printer, they do not
look well on a different printer or at a higher resolution than that for which
they were originally intended. Acrobat Distiller leaves these fonts embedded in
the PDF file, and renders them very poorly. Hence, it is important that the PDF
file does not contain Type 3 fonts.
To produce a good quality PDF, you need to obtain Type 1
(True Type is less well supported by most DVI drivers) versions of all the fonts
that you intend to use, and then inform the DVI driver that it should use them.
Exactly how this is done depends on the driver. For the widely used dvips
driver, it is necessary to make sure that the fonts are listed in the file
psfonts.map or by a map file referenced by the configuration file. With dvips
use the command line options –Pamz –Pcmz to make sure your fonts are embedded
properly. The PostScript (Type 1) implementation of the standard Computer Modern
fonts is now freely available from
AMS.
We recommend that LaTeX users utilize the Times Roman
PostScript font while formatting their documents. This can be achieved by
specifying the Times font in the \usepackage command (see the example below).
However, this procedure will not affect any mathematical fonts, which will
default to Computer Modern in most installations. The package mathptm extends
the usage of the PostScript times fonts to the math environment.
Also,
pdfLaTeX can be used to create the PDF file directly from the *.tex file.
pdfLaTeX uses per default Type 1 fonts. However, any Encapsulated PostScript
(EPS) graphics files must first be converted to encapsulated PDF (EPDF) using,
for example, the
eps2pdf utility. The EPS (in LaTeX) or EPDF (in pdfLaTeX) graphics files can
be included using the graphicx package. The following example illustrates the
use of the times, mathptm, and graphicx packages:
\documentclass[11pt]{article}
\usepackage{times,mathptm}
\usepackage{graphicx}
\begin{document}
Some text…
\begin{figure}[htb]
\begin{center}
\includegraphics[height=2in,width=2.5in,angle=-90]{mygraph}
\caption{This is a figure.}
\end{center}
\end{figure}
More text…
\end{document}
where LaTeX will use mygraph.ps and pdfLaTeX will use
mygraph.pdf. The times, mathptm, graphicx and other packages can be downloaded
from
CTAN.
pdfLaTeX is implemented in the newest release of
MiKTeX, for which the Windows graphics interface
WinEdt is available. It is particularly easy to create PDF files using
WinEdt/MiKTeX: just open the *.tex file and click on the pdfLaTeX icon.
PDF
Creation Tips (Important!!)
-
Use only Type 1 or True Type fonts. Avoid bitmapped, Type 3
fonts.
-
Embed all fonts into the PDF file.
-
Subset fonts at a threshold of 100%.
-
Use the "PRESS-READY" option of Adobe Acrobat to create
your PDF file. Never use the "PRINT-READY" or "SCREEN" or "E-BOOK" option!
-
Create the PDF file on the same computer where the original
document was created. This will insure that the fonts necessary for viewing
and printing the resulting PDF file are available during PDF creation.
-
Do not use Adobe PDFWriter. Use Acrobat Distiller (in the
same package as PDFWriter) or Ghostscript instead. PDFWriter does not produce
acceptable PDF files except under very limited circumstances. Never, ever, use
the PDFWriter if your file contains EPS graphics!
-
When using Ghostscript to create your PDF file, choose the
720 dpi option to assure a sufficiently high resolution of all graphics in
your file and set Options/PDFSETTINGS to /prepress.
-
Since PDF conversions can have many sources of errors
(translating fonts, formats, character sets, etc.), you should always preview
the PDF file you generate to verify its correctness.
Further
Reading
For more information, go to the following links:
NSF PDF Creation Hints and Pointers and
Using Ghostscript to Make PDF Files.
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