PDF Best Practices #4: Fonts Can Make or Break PDFs
Intelligent use determines display and/or printing success
4 February 2002
By Shlomo Perets of MicroType (www.microtype.com)
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Editor's Note: This is the fourth in a series of short, focused "PDF Best Practices" articles by Shlomo Perets, designed to help users create optimal PDF files -- and to understand the various factors involved in doing so.
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A prime reason for using PDF as a format has to do with its ability
to retain graphic appearance and layout; Acrobat's font handling
mechanisms are a key aspect of the portability of PDF files.
When fonts used in the source file PDF are embedded in the PDF,
Acrobat has the original font information at its disposal. If fonts
are not embedded, Acrobat uses the partial font information saved in
the PDF (name, width of different letters, and style characteristics)
to locate the required fonts in the system where the PDF is viewed or
(if no fonts are found) to simulate its appearance using substitution
fonts.
When graphic fidelity is important, a PDF file should be produced so that all fonts used in it are embedded. While font substitution may be reasonably successful in conveying the general appearance of many fonts, it is a design compromise at best as it will never result in a precise match, and with some fonts it may be unacceptable.
To reduce file size when fonts are embedded, font subsetting can be
employed so that only the characters actually used in the PDF will be
embedded. As typically only a small portion of the characters
included in a font is actually used in a specific document, the
result is a significant reduction of font data. This is especially
the case with fonts that store many hundreds or even thousands of
characters (Far Eastern, Unicode or OpenType fonts).
Subsetting will limit or prevent editing operations (text editing or
insert/replace page operations. This is generally not an issue with
PDFs distributed as final documents to be viewed or printed
elsewhere. If these operations are anticipated as part of the
specific PDF life cycle, don't use subsetting. Take into account,
however, that subsetting may take place by default already at the
PostScript driver level.
Fonts that cannot be reasonably substituted by Acrobat must be embedded, regardless of file size issues. This applies to special symbol/logo
fonts, or to fonts with special styles (such as script fonts).
Depending on the specific font characteristics, this may take place
automatically even when embedding is turned off, when Acrobat
identifies such a font.
To further reduce file size related to font storage, you can specify
that the base-14 fonts will not be embedded. These include the
Helvetica, Times, Courier standard font families (regular, italic,
bold, bold italic), Symbol and Dingbats. Acrobat Reader installations
include fonts that fully match these functionally (identical
character widths, but a slightly different design). When you decide
not to embed fonts, inspect the results of font substitution, which
will equally apply to viewing and printing. This can be done with
View > Use Local Fonts. When this setting is disabled, fonts that are
not embedded in the PDF will be simulated, even if they are installed
in the computer where the PDF is viewed. Notice that in some cases,
font substitution results in serious spacing problems or highly
distorted letter shapes.
Example 1: Actual Fonts (click image for full example)
Example 1: Substituted Fonts (click image for full example)
Example 2: Century Schoolbook - Actual Fonts (click image for full example)
Example 2: Century Schoolbook - Substituted Fonts (click image for full example)
Example 3: Frutiger Ultra Black and Myriad - Actual Fonts
Example 3: Frutiger Ultra Black and Myriad - Substituted Fonts
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Font Formats
Acrobat Distiller 5 works equally well with all common font formats:
- PostScript (Type 1)
- TrueType
- OpenType
PostScript Type 3 fonts, in use by some TeX installations, are to be
avoided -- as display of resulting text in PDFs will be slow and poor,
file size will be larger than it should, and text may not be
searchable. Bitmapped Type 3 fonts are sometimes encountered in the
PDF even though the original fonts used are valid PostScript or
TrueType fonts -- this is usually a result of a malfunctioning
PostScript driver (especially on Windows NT).
When purchasing new fonts for use with your authoring applications,
make sure that there are no embedding restrictions.
To view a list of fonts used in a PDF file, choose File > Document
Properties > Fonts. When first opened, this displays a list of fonts
used in the specific page being viewed (including font format and
embedding/subsetting status). Click the "List All Fonts" button to view
a list of all fonts used in the document.
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Typographic Settings
Be aware that some advanced typographic features (such as ligatures,
old-style figures and small caps), if supported by your authoring
program and fonts used, may impair Acrobat's text interpretation and
affect text-related functions: Find and Search, Copy/Paste, bookmark
created from selected text and automatic web link creation. Increased
letter spacing can add extra spaces and will also adversely affect
text.
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Use Only Fonts That Are Fully-Installed
Make sure that you only use fonts or styles that are available as
standard installed fonts. Acrobat Distiller cannot embed font
information in a PDF if the font data is resident on a printer; the
printer driver enabling these fonts provides partial data only (font
name and metrics).
Likewise, when using bold variations with fonts that do not have a
bold version installed, some authoring applications (including Word
and FrameMaker) will "simulate" the missing weight, together with the
PostScript driver, through duplication of the text instance to be
"bolded" a number of times, using very small offsets -- resulting in a
bolder appearance. This is not recommended aesthetically, as a bold
font uses a different design; it also results in display and
text-related problems at the PDF level, where the bolded text resides
as multiple instances of the word.
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Which Font Styles Should Be Used?
This relates to aesthetics, and may be highly subjective. When PDFs are designed primarily or even solely for print purposes, there are no display-related limitations. However, when a PDF is to be displayed on screen, text set in a small size using fonts with delicate serifs or curves may be distorted due to the low resolution of the screen, to the extent of disappearing. Many italic fonts will not survive the screen's low resolution. Black (heavy) font weights -- serif or sanserif -- will also be distorted (some shapes clogged). However, some of these fonts may work well if used in a larger font size (such as in headings). Given the screen characteristics, extra attention should be paid to the combination of factors affecting readability: font, size, line spacing and line length.
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Font-Related Aspects in PDFs Included On the Acrobat 5 CD
The vast majority of PDFs in the Acrobat 5 CD use only base-14 fonts.
With a few exceptions, these fonts are not embedded -- which is fine
for general- purpose use, as Acrobat Reader has matching built-in.
The custom logo font is embedded -- this could have been the case even
if no fonts were selected for embedding (as Acrobat Distiller will
automatically embed fonts it identifies as special fonts).
Running text in most documents is set in 11-pt Helvetica; a few
documents use 12-pt Times. Code fragments are set in 10-pt Courier
(sometimes in larger sizes).
This combination of fonts is probably the safest you can have (but
this should not be construed as a recommendation for all PDF
producers to solely rely on fonts from this minimum set.)
The Acrobat Help and PDFMaker Help files use a different design,
based on 11-pt Myriad for regular text (embedded).
In a few PDFs, larger-size fonts used for main headings were
transformed into bitmaps. In the BatchSequences.pdf file, for
example, the "Batch Sequences" heading cannot be selected as text,
and will not be located by the Find or Search functions. This may be
the result of an inadvertent setting in the PostScript driver used
(or a bug).
The PDF Reference (version 1.3) Manual, second edition, is also
included in the Acrobat 5 CD (this specific PDF was reviewed
separately in terms of its online use). Fonts used in the title page
(Myriad and Caecilia Heavy) are not embedded, and are simulated using
Acrobat's built-in Adobe Serif/Sans MM "chameleon" fonts. Apparently the same PDF
was used for the book production. As the fonts were not available on
the production system, the simulated fonts can be identified in the
title page of the printed book (first printing, July 2000).
Example 4: PDF Reference - Actual Fonts
Example 4: PDF Reference - Substituted Fonts
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