Best Practices #2: Creating Effective Acrobat Bookmarks

Editor’s Note: This is the second in a series of short, focused articles designed to help users create optimal PDF files — and to understand the various factors involved in doing so.

Acrobat’s bookmarks can be a particularly efficient navigation
mechanism that provides easy access to common locations and actions.
With nesting and expand/collapse capability, bookmarks create a
constant conceptual display of the document’s structure. Starting
with Acrobat/Reader 5, bookmarks can have color/font style
properties, so that specific bookmarks can be emphasized.

Bookmarks do not complicate display and printing aspects of the PDF
file (as they, together with all interactive features, are ignored
when the file is printed). Bookmarks are either created automatically
when using common authoring applications (PageMaker, FrameMaker, or
Word with PDFMaker, to name a few) and/or manually in Acrobat.
However, in both cases, efficient bookmarks are not guaranteed. This
article provides guidelines for bookmarks that are useful to the
readers of PDFs.

What Should Be Bookmarked?

Bookmarks should be available for all important items in your PDF. In
business or technical documents, bookmarks typically include up to 4
top-level headings. As a minimum, all top items should be included:
chapter headings, all frequently accessed locations such as Contents,
Index, List of Figures or Tables (which may be used to locate the
required item and jump directly to it using a link).

When producing a document collection, be consistent across the
collection and also add bookmarks leading from one document to the
others (such as main menu and/or other chapters).

While bookmarks commonly point to destinations within the current
PDF, they can also point to other PDFs, and can be used for other
related purposes:

  • Linking to web sites and e-mail addresses

  • Launching external data files

  • Specifying various Acrobat actions, for example:
    Search (all Acrobat actions can be assigned to bookmarks)

  • Linking to multimedia items (video/sound)

Does a list of bookmarks replace a table of contents?

No. Bookmarks are inefficient when expanded to show the entire
hierarchy, since they become a very long list that must be scrolled.
In addition, expanding the bookmarks (if initially collapsed) has to
be done manually for each and every bookmark.

A detailed table of contents provides a listing of all topics at one
glance, whether it is one page long or spans several pages. Many
readers inspect the table of contents when opening a book – printed
publication or an online document – trying to find items or
understand the structure. The table of contents should therefore
provide a listing of all topics. The bookmarks can be a subset of the
table of contents with fewer levels, or identical in depth. However,
it makes no sense for the table of contents to be less detailed than
the bookmark list. Supplying both bookmarks and a table of contents
provides the reader with multiple options.

Another consideration is that many PDFs are printed, in which case a
Table of Contents is essential. Often, with huge documents, even if
the PDF itself is not printed, the Contents pages may be printed and
kept for handy reference.

A bookmark to the table of contents is essential. Even if the table
of contents is at the beginning of the document, a cover page,
disclaimer, warranty and other front matter items typically precede
it. A Contents bookmark alerts the reader to the existence of the
table of contents and makes it easy to access regardless of the page
currently open.

The table of contents must also have hyperlinks, so that the user can
jump directly to the topic chosen, without having to locate the topic
in the bookmarks.

Order of Bookmarks

Bookmarks to headings should typically reflect the order of the items
in the book. However, there are exceptions to this rule. When there
are too many bookmarks and the entire list cannot be displayed
without scrolling, even when all top items are collapsed, a bookmark
to the index may be hidden at the end of the list. In such cases, it
is recommended to place the Index bookmark at the top of the list,
perhaps after the Contents bookmark. (It is also helpful to have
subordinate bookmarks to letters within a lengthy index, so that it
is easy to jump to entries starting with ‘M’, for example).

In publications with many titled tables and figures, specific
bookmarks for each of these may be useful. However, when all items
are in the order of appearance in the document, bookmarks to figures
or tables will be spread, showing under headings of different levels,
most of which are likely to be collapsed. Creating separate
‘Figures’, ‘Tables’ or ‘Equations’ bookmarks with all relevant
bookmarks subordinate to them is much more efficient, similar to such
lists in printed books.

Easy to Identify

Bookmark text should be easy to identify. The bookmark pane is
relatively small and in most cases will not be wide enough to display
complete headings. Starting with Acrobat 4, a tool tip for the
bookmark being pointed to is displayed, showing the full text if it
is too long to fit in the bookmark pane. But despite this useful
feature, the more meaningful text can be displayed, the better.

Common situations that cause the actual content of the bookmark text
to be partially pushed out of view include:

  • Insignificant or non-unique text at the beginning,
    such as The, Chapter, Appendix (which could be shortened or omitted,
    for example ‘1: Filing Principles…’ instead of ‘Chapter 1: Filing
    Principles …’, or ‘B: System Specifications…’ instead of ‘Appendix B:
    System Specifications’).

  • Heading numbers – despite the usefulness of heading
    numbers in the document itself, both for locating material quickly
    and for easy comprehension of the hierarchy level, in bookmarks the
    text is much more important. Numbering, particularly in lower-level
    bookmarks of documents that use multi-level numbering (which have
    less space due to indentation), may use a significant part of the
    bookmark pane. And, if you have included a table of contents in your
    document, the numbering will be present there and can be omitted in
    the bookmarks.

  • All-caps text causes text to be less readable. While
    this is true with regard to headings too, some style guides require
    all caps for top-level items. Depending on the authoring software
    being used, it may be possible to have the text in the page shown as
    all caps, while the bookmarks can use upper- and lower-case text.

Open Mode, Hierarchy and Initial Collapse/Expand State

Generally, if bookmarks are created for a PDF, it is a good practice
to have an initial view of ‘Bookmarks and Page’ – otherwise some
readers may not be aware of the availability of the bookmarks.

The bookmark hierarchy should match the document’s heading hierarchy,
unless you have a very good reason for breaking this rule.

It is also important that the opening collapse/expand state displays
the main items for the entire publication, so that top-level items
are visible, with other levels collapsed – resulting in a much neater
structure. In addition, when all or most bookmarks are expanded, the
list is too long and most of it is hidden initially, so that
important items may never be used (as scrolling long lists is not
typically done). In bookmark structures where ‘Chapter’ bookmarks are
the top ones, bookmarks should be initially collapsed under the first
level; in structures where there are ‘Part’ or ‘Book title’ bookmarks
as the first level (with chapters as the second level) – bookmarks
should be collapsed under the second level.

When saving a PDF in Acrobat, the current state of bookmarks is
preserved. Thus, it is important to pay close attention to the
collapse/expand state just before the ‘last’ Save (or better yet,
Save As). Of course, exceptions to the collapse/expand level set
automatically by the authoring application can be made, as long as
these are intentional!

Bookmarks use a single system font; it is not possible to have
variations in fonts/styles within a bookmark. Some special characters
may suffer as a result – Greek letters or scientific symbols in a
heading, for example, will be carried over to the bookmark text as
characters in the standard font. While Acrobat itself supports
Unicode encoding in bookmarks since version 4.05, authoring
applications are slow to implement the required mechanisms to support
this.

Control characters should not be included in the bookmark text, yet
some authoring applications (particularly FrameMaker) transfer
whatever is included in headings when bookmarks are created
automatically. Common control characters include non-breaking spaces,
special fixed spaces, non-breaking hyphens, suppress hyphenation
characters and new line characters. Version 3 and 4 of Acrobat either
ignored such characters in bookmarks or displayed them as spaces. In
Acrobat/Reader 5, they are displayed as boxes.

This is true even when a PDF was created using Distiller 3 or 4 and
is being displayed in Acrobat Reader 5. Beware of this unsightly
phenomenon that may appear in some of your old PDFs when users open
them with Reader 5.

Color and Font Properties

One of the few additions to Acrobat 5.0 as far as users of Acrobat
Reader are concerned is bookmark color and font style properties.
Unique colors/styles are useful as a way to highlight special
bookmarks (such as What’s New), or to designate bookmarks with
external destinations (other files or web links). Using these
properties can also be helpful as a way to distinguish between
hierarchy levels.

Spelling

This may sound obvious, but there is nothing more embarrassing than a
bookmark with a typo, displayed at all times. When bookmarks are
created automatically from paragraphs, we can assume that the
document itself was checked for errors before output to PDF. When
bookmarks are added manually, double-check the bookmark text. (When
creating a bookmark to a heading manually in Acrobat, the paragraph
can be selected first so that its text is retrieved without having to
retype it).

Remedies

Many of the above recommendations do not necessarily have to be
implemented manually in Acrobat. Maximize the use of settings
provided with your authoring tool and use add-ons that automatically
remove numbering and redundant text, add color/style to your
bookmarks, control initial collapse state, handle special characters
or reorder figure, table or equation bookmarks.

Review of the use of Bookmarks in PDFs in the Acrobat 5 CD

The Acrobat 5 CD contains various PDFs, including the Acrobat help
files and the Acrobat SDK documentation (Acrobat SDK is also
available in partners.adobe.com) – 42 PDF files in total.

With one exception, all PDFs were authored in FrameMaker, which is
capable of generating bookmarks from designated paragraph styles
(similar or better capabilities are available with other popular
authoring tools). With a few exceptions, it does not seem that
bookmarks were given thought beyond their automatic rendering.
Automation is great, but care has to be taken to make the most out of
the settings available; if necessary, additional techniques – manual
or automatic – have to be employed.

Inspecting the use of bookmarks in the Acrobat 5 CD PDF collection, I
reached the conclusion that it was not inspiring. Review the same
PDFs and make up your own mind!

Bookmark composition and style is not consistent in the different
PDFs, even though many are very similar in structure:

In about two thirds of the PDFs, the document’s title is used
as the first bookmark.

  • Bookmarks to Contents are available in most PDFs but
    not in all (e.g. Spelling API, ADM Reference Guide). The pdfmark
    reference manual is present twice on the CD – once as part of the SDK
    and once in Acrobat Help documents; one version has a Contents
    bookmark, the other does not.

  • The Acrobat SDK has an interactive Roadmap chart
    included in most of documents. In most PDFs where the Roadmap is
    present, there is a bookmark pointing to it, but a few PDFs (Acrobat
    Development Overview, Core API Overview, Distiller API Reference) do
    not have one. (This was fixed in SDK PDFs available for individual
    download, dated June 25)

  • The 2-page index in the PDFMaker help PDF file has a
    bookmark with subordinate bookmarks for the index letters, whereas
    the bookmark pointing to the 17-page index in the Acrobat Core API
    Reference does not have these.

  • The treatment of the top-level numbered bookmarks is
    different in otherwise-identical PDFs included twice in the CD
    (Acrobat Distiller Parameters, present once in the SDK and once in
    the Help).

Bookmark nesting and collapse/expand state also vary. This may be
related in part to the way FrameMaker generates bookmarks, with a
default collapse/expand state that seems whimsical (there is some
arbitrary logic behind it, having to do with the number of
subordinate bookmarks). Nonetheless a simple fix in Acrobat could
have remedied this.

In a few PDFs, collapse/expand state seems to be ‘random’ (that is,
the bookmark state used by the author when the PDF file was last
saved).

One could expect that PDFs supplied with Acrobat 5 would be taking
advantage of the new bookmark color/style properties. I was able to
find only one bookmark that looked different: the ‘What’s New For
5.0′ bookmark in the Acrobat JavaScript Object Specification PDF.

All bookmarks in the Acrobat 5 CD PDFs point to paragraphs in the
current PDF. Acrobat functionality does not limit bookmarks to this
purpose, and the document creators could have added:

  • Bookmarks to the Acrobat News or Technical Updates
    web pages, where readers can possibly learn about a new version of
    the document available for download

  • Bookmarks that when clicked open a feedback form that
    can be e-mailed instantly using the user’s mail client

  • Bookmarks to other PDFs (for example, the Roadmap
    could have been produced professionally once and then linked to by
    bookmarks in all other PDFs, instead of being physically duplicated
    in each manual, which has a undesirable side-effect when using Search)

  • A ‘Popular Searches’ bookmark, with subordinate
    bookmarks that have commonly-used pre-defined Search terms. Click the
    bookmark, and you get an instant Search Results for the pre-defined
    item.

Specific Examples

Acrobat Help – AcroHelp.pdf

When opening the Acrobat Help file, four top-level bookmarks are
visible: Using Help, Contents, Index and Legal Notices. To see
specific topics, one has to click the Contents bookmark, and repeat
this each time the PDF is opened. It would have made sense to save
the PDF with the Contents bookmark expanded, so that second-level
items under it are visible with no need for an additional click, or
to otherwise set the two top levels bookmarks to be visible.

The Contents bookmark in the Acrobat Help file, when clicked, takes
us to a single page Contents, which only lists the chapters – so that
a comprehensive list of all topics in the document is not available,
unless one is willing to expand all bookmarks.

An example for a box in the bookmark text is available under
Contents > Creating Adobe PDF files > Converting Asian Text to Adobe
PDF > Working with Japanese ATM Type 1 Fonts.

PDFMaker help PDF – Help/ENU/PDFMaker.pdf

In the PDFMaker help PDF, which has a structure similar to the
Acrobat help PDF, the chapter bookmark is subordinate to the
collapsed Contents bookmark. Not much logic here…

PDF Reference Manual, 2nd Edition, v.1.3

When opening the PDF Reference manual included in the Acrobat 5 CD,
the bookmark branch starting with Appendix H is entirely expanded,
for no good reason.

Incidentally, in that same expanded Appendix H, under ‘H.3
Implementation Notes,’ several bookmarks show boxes for various
reasons, including non-breaking spaces (1.2, Type 4), discretionary
hyphens (4.8.4, Dictionaries), suppress hyphenation characters (4.9,
X objects).

The three-level numbering carried to the bookmark text is not a wise
use of the prime real estate of the bookmark pane.

Core API Reference – Core_API/CoreAPIOverview [PDF: 17 MB]

The Contents bookmark in the 2755-page long Core API Reference points
to a confused table of contents slightly longer than one page, which
lists only the main categories (with items of different levels using
the same format). To make the barely useful Contents page even less
useful, the few items that it has are not hyper-linked (links will be
treated in a separate Best Practices article).

Summary

There are many different ways in which the bookmarks in the Acrobat 5
PDFs could have been more useful, attractive and easier to use. The
limitations demonstrated in these PDFs are not related to Acrobat’s
capabilities as a tool, but to the lack of someone taking a bird’s
eye view of the collection as a whole and making decisions to be
followed consistently.

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About the Author: Shlomo Perets

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