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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