Graphics Programs Reference
In-Depth Information
Adobe
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Incorporated
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Annotations and Hyperlinks
Annotations are used in PDF to add comments or interactive elements outside of the
page content itself. Each viewer application (for example Adobe Reader or Mac OS X
Preview) may display these annotations in a different way, even changing between
software versions, so the exact visual effect cannot be relied upon. The annotations do
not affect the printed output.
One or more annotations may be associated with each page using an array under the
entry
/Annots
in the page dictionary. Each annotation is a dictionary. The more im-
portant entries are described in
Table 7-4
. Each type of annotation has additional en-
tries in this dictionary.
Table 7-4. Entries in an annotation dictionary (*denotes required entry)
Key
Value type
Value
/Type
name
If present, must be
/Annot
.
/Subtype
*
name
The type of this annotation.
/Rect
*
rectangle
The location and size of the annotation in default user space units.
/Contents
text string
The textual content of this annotation, or if none, an alternate human-readable description.
We'll look at two kinds of annotations:
text annotations
which can be used to add
comments, and
link annotations
which are used to make hyperlinks within a document.
There are many other types for drawing on the document, highlighting text and adding
printer's marks. In
“File Attachments” on page 96
, we use
file attachment annota-
tions
to add attachments to individual pages.
First, a text annotation. Here, the
/Subtype
is
/Text
. The code is shown in
Exam-
ple 7-3
. We set the extra annotation dictionary entry
/Open
to
true
to indicate the note
will be visible when the document is opened. The background color is set to White
with the
/C
entry.
