String Objects
Strings as they are serialized into PDF are simply series of (zero or more) 8-bit bytes
written either as literal characters enclosed in parentheses, ( and ), or hexadecimal data
enclosed in angle brackets (< and >).
A literal string consists of an arbitrary number of 8-bit characters enclosed in paren‐
theses. Because any 8-bit value may appear in the string, the unbalanced parentheses
( ) ) and the backslash (\) are treated specially through the use of the backslash to escape
special values. Additionally, the backslash can be used with the special \ddd notation to
specify other character values.
Literal strings come in a few different varieties:
ASCII
A sequence of bytes containing only ASCII characters
PDFDocEncoded
A sequence of bytes encoded according to the PDFDocEncoding (ISO 32000–
1:2008, 7.9.2.3)
Text
A sequence of bytes encoded as either the PDFDocEncoding or as UTF–16BE (with
the leading byte order marker)
Date
An ASCII string whose format D:YYYYMMDDHHmmSSOHH’mm is described in ISO
32000–1:2008, 7.9.4
Dates, as a type of string, were added to PDF in version 1.1.
A series of hexadecimal digits (0–9, A–F) can be written between angle brackets, which
is useful for including more human-readable arbitrary binary data or Unicode values
(UCS-2 or UCS-4) in a string object. The number of digits must always be even, though
white-space characters may be added between pairs of digits to improve human read‐
ability. Example 1-4 shows a few examples of strings in PDF.
Example 1-4. Strings
(Testing) % ASCII
(A\053B) % Same as (A+B)
(Français) % PDFDocEncoded
<FFFE0040> % Text with leading BOM
(D:19990209153925-08'00') % Date
<1C2D3F> % Arbitrary binary data
4 | Chapter 1: PDF Syntax
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