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"Portability is the cornerstone of the PDF. However, since its inception,
the PDF’s foremost characteristic has been shaken by its own popularity and evolution. But what are
Source : Amyuni Technologies
Missing PDF Fonts: Why It Happens and What You Can Do About It
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is also known as :
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Edit pdf Easily,
This document is the first of two that will look at some of the challenges
faced by developers and non-developers who work with PDF technologies and who
are curious about what causes fonts in a PDF to render incorrectly or even go
missing. Specifically, these documents provide an overview of some of the
problems associated with missing font information in PDFs.
The first document presents the Portable Document Format as well as industry
terms and concepts related to that format. The problem of missing font
information will also be introduced. The second document expands on those terms
and concepts and explores some of the common scenarios in which PDFs are either
missing partial or entire font information.
Brief Overview of PDF
The Portable Document Format was originally conceived in 1991 as the Camelot
Project, by Adobe’s co-founder Dr. John Warnock. Inspired by the device
independence of PostScript, Dr. Warnock wanted to develop a technology that
could accurately display and print electronic documents across different
operating systems, hardware, or applications. His answer was the PDF.
Unlike its predecessor (i.e., PostScript), PDF was first and foremost a file
format and not a programming language. Although PDF evolved from PostScript, the
primary difference is that PostScript is a true page description language and
PDF is not. PDF does not contain programming constructs such as looping,
control-flow constructs, or variables. Rather, PDF was envisioned to go further
than PostScript by being able to describe how pages behave and what type of
information a document could contain. Years later, the PDF would encompass
complex features and functionalities such as search capabilities, audio, and
On July 1, 2008, PDF became an open standard published by ISO as ISO 32000-1:
PDFs are essentially collections of data objects organized in a hierarchical
manner that describe how one or more pages in a document must be displayed.
These data objects can describe a page, a resource, other objects, a sequence of
operating instructions, and so on. Furthermore, a data object can reference
other objects and be referenced by other objects (i.e., an object can be a
parent object and a child object at the same time).
PDF documents contain four main types of objects that define its structure:
- the document catalog object
- page objects
- page content objects
- document and page resources
The document object typically contains a cross reference table and page
objects. It can also contain elements such as document information, named
destinations, thumbnails, and bookmarks.
Page objects can contain one or more content objects as well as several other
types of elements such as page cropping information, hyperlinks, article
threads, file annotations, form fields, digital signatures, and child pages in
the document. Page objects also contain references to all the resources used by
Content objects contain marking operators (i.e., drawings) and use resources
such as fonts, images or color spaces that are needed to fully render the page.
PDF defines a number of resource objects such as fonts, images, color spaces,
patterns, etc. Fonts are needed to render text, color spaces represent colors
used in the document, patterns define how backgrounds are painted, etc.
PDFs are sectioned into four separate areas:
- the header
- the body
- the cross-reference table (xref)
- the trailer
The header contains a comment that identifies the nature of a PDF document
and the specifications to which it adheres. For example, the comment outlined in
Figure 1 indicates that the document conforms to Version 1.7 of the PDF
Figure 1. Header
The body of a PDF is where the content objects in the document are located.
These objects include text streams, image data, fonts, annotations, and so on
(see Figure 2 on page 4). The body can also contain numerous types of invisible
(non-display) objects that help implement the document's interactivity, security
features, or logical structure. Each object has three essential components: a
numerical identifier, a fixed position (also known as an offset), and its
Figure 2. Examples of Objects in the Body
7 0 obj
/BaseFont /CGFGAX+TRReservedPIFont,BoldItalic/FirstChar 32
220 265 187 567]
/FontDescriptor 8 0 R
8 0 obj
/FontBBox [ -140 -269 1027 906 ]
/FontFile2 9 0 R
The Cross-Reference Table
The cross-reference table (see Figure 3 on page 5) lists the locations of all
the objects in a PDF document. The cross-reference table is divided into
sections where each section begins with the starting and ending identifiers of
the objects in that section. With the cross-reference table, a PDF parser can
randomly identify object offsets and quickly access object locations throughout
the document without having to read the entire file.
Figure 3. XREF Table
0000000000 65535 f
0000000067 00000 n
0000001244 00000 n
0000001264 00000 n
0000001370 00000 n
0000002027 00000 n
0000009301 00000 n
0000009424 00000 n
Even though the trailer is technically the end of a PDF document, it is the
first entry point that applications use to access the essential components of a
PDF. The trailer contains pointers that parsers and applications use to locate
the cross-reference table and other important objects in a PDF.
Examples of important objects include the root object (that identifies the
beginning of a page tree) and info objects (that contain vital metadata).
Figure 4. Trailer
/Root 4 0 R
/Info 99 0
Terms and Concepts
Before outlining the challenge of missing fonts in PDFs, it is important to
review some of the underlying concepts and technologies that will be used
throughout the rest of the documents.
Glyphs and Characters
Norman Walsh defines a glyph as: “the actual shape (bit pattern, outline) of
a character image. For example, an italic “a” and a Roman “a” are two different
glyphs representing the same underlying character. In this strict sense, any two
images which differ in shape constitute different glyphs.” Consequently, glyphs
are organized into different types of fonts. By contrast a character is an
abstract symbol that is given shape through a glyph’s design.
A character code is a digit associated to a specific character. For example,
a character with the character code “37” displays a different glyph depending on
its typeface (e.g., Calibri, Arial, Webdings, etc). At the most basic level, an
application that renders PDF documents only needs to access the character codes,
the font information, and the mapping from the character code to the font
information. With this information the rendering application extracts the key
graphical data to draw a glyph on an output device such as a screen or printer.
Fonts and Typefaces
Although the difference between fonts and typefaces may seem trivial to some,
confusion still lingers within some development circles, where the term font
families is commonly used when referring to typefaces. This is why it is
important to clarify some of the upcoming terms.
A font is a comprehensive group of characters with a specific style of type.
It includes the letter and number set, special characters, as well as
diacritical marks (accents). Furthermore, a font specifies the member of a type
family such as roman, boldface, or italic type.
Within the context of PDF software development, a font is a PDF object
commonly referred to as a font object (see Figure 5 on page 7), font dictionary
or font data file. A font object contains a set of glyphs, characters, or
symbols (such as wingdings). The font object also identifies the font program
and contains additional information such as its properties.
Figure 5. Example of a Font Object
7 0 obj
/BaseFont /CGFGAX+TRReservedPIFont,BoldItalic/FirstChar 32
711 416 440 440 440 440 258 258 258 258 494 550
493 493 493 493 493 220 489
543 543 543 543 220 542 438 ]
8 0 R
8 0 obj
/FontBBox [ -140 -269 1027 906 ]
9 0 R
9 0 obj
/Length 10 0 R
By contrast, a typeface specifies a consistent visual appearance or style
which can be a "family" or related set of fonts. Arial, Tahoma, or Helvetica are
examples of typefaces. A typeface can contain a series of fonts. For example, a
typeface such as Helvetica may include roman, bold, and italic fonts.
Font Technologies: Laying the Foundation
From their inception in the mid-1980s, font technologies have helped jump
start the desktop publishing revolution and have enabled the written word to
cross over to digital typesetting mediums.
Standards expanded, new font technologies emerged, and within a few years,
the world of PDF had become more complex. Not only did those who developed PDF
viewers and convertors had to adapt to the emerging trends within the PDF
industry, but they also had to support the rising demands for different
Asian languages presented PDF developers with new challenges as the existing
font technologies could no longer sufficiently answer increasing font
complexities. These new challenges helped push font technologies and developers
Although digital fonts are generally grouped into three format types (namely,
bitmap, stroke, and outline (vector) types), this paper will focus on outline
Unlike bitmap fonts that are collections of raster images of glyphs, outline
fonts (also known as scalable fonts) are collections of vector images. This
means that outline fonts describe glyphs using points that are interpreted as
lines and curves.
The advantage to using vector images is that they can be scaled to varying
sizes without losing too many details. By contrast, bitmap fonts lose their
detailed edges and often appear jagged or choppy when resized (Figure 6 on page
Figure 6. Font Type Scalability Differences
Hinting: When Scalability Isn’t Enough
Even though outline fonts are scalable, there are many instances in which
proper rasterization can be compromised. For example, different applications,
output devices, or printers can affect rasterization. To address this problem
hinting technologies were developed. Hinting is additional mathematical
information added to a font to ensure it retains its visual integrity when
rasterized under various conditions.
Type 1 (PostScript)
Developed by Adobe Systems, PostScript fonts were developed to answer the
demands of emerging laser printing technologies at the time. Using a subset of
the PostScript language, Type 1 fonts contain an organized collection of
procedures to describe glyph forms.
In addition, glyph outlines were interpreted by Type 1 fonts using a field of
mathematical analysis known as (cubic) Bézier curves. When first introduced,
Type 1 fonts were the first to include proprietary hinting technology to improve
their display capabilities. Type 1 fonts store information in two files. One
file contains the character outlines (referred to as printer fonts) and the
other contains the character information to display on screen.
Type 3 fonts are essentially the same to Type 1 fonts except that they don’t
include hinting technology. While Type 1 fonts only use a subset of the
PostScript language, Type 3 fonts encompass most of the PostScript language.
This makes Type 3 fonts capable of displaying more elaborate designs and
ligatures than Type 1 fonts. However, the added weight of the PostScript
language into Type 3 fonts also makes their file sizes larger. They therefore
take up more memory. Because Type 3 fonts use bit-mapped technology instead of
hinting, they often produce poorer display results when they are scaled.
Developed by Apple Computers, TrueType fonts are similar to Type 1 fonts, but
include some important differences. Like Type 1 fonts, TrueType also uses Bézier
curves to describe glyph information; however, TrueType employs quadratic
mathematics rather than cubic.
Another difference between TrueType and Type 1 is that TrueType contains both
the screen and printer font data in a single file. In addition, hinting
information is stored inside the font file. This additional information makes
TrueType fonts larger than their original PostScript rivals.
Unlike Type 1 files, however, which are composed of a subset of the
PostScript language, TrueType font files are composed of structured tables. Each
table contains the necessary information that applications or PDF viewers need
to use and display a font. Tables also contain information to ensure that glyphs
are displayed correctly when there are different types of internal encodings
used in a document.
OpenType fonts bring together some of Type 1 and TrueType technologies into
one cross platform format. OpenType’s character encoding is based on Unicode and
as a result, can support up to 65,536 glyphs, OpenType offers more development
flexibility especially when working with Asian character sets and more
sophisticated Roman glyphs that may use non-lining numerals, small caps,
fractions, ligatures, and swashes. Like TrueType, an OpenType font contains all
of its outline, metric, and bitmap information in a single file.
Font File Structures
In addition to their technological differences, fonts can also be categorized
according to how they are structured as PDF objects. Generally, fonts can be
- Simple Fonts
- Composite Fonts
PDFs contain font objects (see Figure 5 on page 7) that essentially act as
wrappers for embedded font programs that contain the actual font data. Font
programs can be TrueType, OpenType, Type 1, and so forth. Font objects also
contain a number of properties and descriptions of the font data in order to
enable PDF applications and viewers to use the font in the document.
Simple Fonts use a single byte of information to represent a glyph. As a
result, a maximum of 256 (28) different glyph representations are possible. The
Simple Font category includes the original instances of Type 1 and TrueType
Because of their 256 character encoding limitation, Simple Fonts could not
support complex Asian glyphs, where a typical Japanese font can have over 7,000
Kanji, Katakana, and Hiragana characters, or non-horizontal writing.
The solution was the development of Composite Fonts (or CID fonts). Unlike
Simple Fonts, Composite Fonts are multi-byte and can thus contain an arbitrary
number of glyphs. As a result, Composite Fonts are able to support a wider range
Composite Font technologies enable developers to use any number of base fonts
and create new composite fonts. Composite font technologies also enable
developers to include two sets of character spacing details (metrics) in fonts.
One metric can be used for horizontal writing mode and another for vertical
Aside from their ability to handle complex glyphs, Composite Fonts are also
flexible and expandable.
A CMap is an ASCII text file that contains the PostScript language
instructions required to map character codes to CID codes used by Composite
Fonts. For example, after a character code is processed (from a keyboard input),
the CMap file maps the character code to a corresponding
Character Identifier number (CID). The CID code is then passed on to the
Composite Font which will in turn generate the appropriate glyph. As we shall
see in the next document, CMap files can also be missing and impact proper PDF
To display, print, or process a PDF accurately, it must contain the necessary
font information. If font information is missing, recipients may not be able to
display or edit the document properly or, worse, applications may not be able to
process the PDF at all.
Embedding fonts in a PDF ensures that they display and print exactly from one
system to another as the author intended. The following sections will look at
how fonts are embedded in PDFs and introduce the upcoming subject matter for the
Full Font Embedding
The first method of embedding fonts is full font embedding. Full font
embedding effectively makes the font part of the PDF thereby preventing font
substitution when recipients need to display or print a PDF. Essentially
recipients don’t need the same fonts to view or edit the document. This method
is advisable in situations in which modifications to the PDF are expected.
Full font embedding can also potentially help avoid some of the problems
associated with missing system fonts and ensure optimal viewing regardless of
the system and platform. In an ideal PDF world, fully embedding all fonts would
reduce many development woes.
The main drawbacks to full font embedding are file size and licensing issues.
Every embedded font makes the document larger, especially if it contains
Chinese, Japanese, or Korean (CJK) fonts, which can be problematic. In
fact, CJK fonts are rarely fully embedded due to their large character sets.
Also, fully embedded fonts can be extracted and used outside of the PDF file. As
a result, this font extraction can create the potential of unlimited font
distribution and violate the licensing policy of the font manufacturer. The
solution then is to partially embed fonts in a document.
Partial Font Embedding (Subsetting Fonts)
Unlike full font embedding, subsetting a font only embeds the glyph
definitions for the characters used (i.e., that are displayed in the PDF).
There are three main reasons one should subset fonts. First, as previously
stated, PDFs are primarily for content exchange and viewing. PDF is not an ideal
editing format, despite the popularity of PDF editing programs available on the
Internet, and it is generally assumed (rightfully or wrongfully) by the PDF’s
creator that the recipient will not modify the document’s contents. As we shall
see in the following document, editing a PDF is not always a straightforward
Second, subsetting fonts reduces document size. For example, the size of the
font “Arial Unicode MS” is nearly 20MB; however, subsetting this font to show 10
Kanji characters would instead only add approximately 25KB to the PDF. In cases
where CJK fonts are used, full embedding all fonts would result in
problematically very large files.
Third, subsetting of fonts avoids licensing issues because the font then
becomes unusable for other purposes then rendering the document which is often
permitted by the font licensors. The draw back with partially embedded fonts is
that if recipients do not have the fonts on their system, they will not be able
to edit the document or will be very limited in their ability to edit text. This
is where the problem of missing fonts begins to emerge.
When Fonts Go Missing
Now that some of the key PDF and font concepts have been reviewed, the
different problems that can occur when font information is missing can be
The following document (Part 2) will explore how problems associated with
missing font information can start right at the source, with the creation of the
PDF document itself. These problems include full and partial font embedding,
incomplete font information in TrueType fonts, and missing CMap files.
Walsh, Norman. "Frequently Asked Questions About Fonts."
14 August 1996. <
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