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.