Editing PDF (section)

=== Text ===

Text in PDF is represented by ''text elements'' in page content streams. A text element specifies that ''characters'' should be drawn at certain positions. The characters are specified using the ''encoding'' of a selected ''font resource''.

A font object in PDF is a description of a digital [[typeface]]. It may either describe the characteristics of a typeface, or it may include an embedded ''font file''. The latter case is called an ''embedded font'' while the former is called an ''unembedded font''. The font files that may be embedded are based on widely used standard digital font formats: [[PostScript fonts|Type 1]] (and its compressed variant CFF), [[TrueType]], and (beginning with PDF 1.6) [[OpenType]]. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators. <!--- Type 3 bit is awkward and should be cleaned up --->

Fourteen typefaces, known as the ''standard 14 fonts'', have a special significance in PDF documents:

* [[Times Roman|Times]] (v3) (in regular, italic, bold, and bold italic)
* [[Courier (typeface)|Courier]] (in regular, oblique, bold and bold oblique)
* [[Helvetica]] (v3) (in regular, oblique, bold and bold oblique)
* [[Symbol (typeface)|Symbol]]
* [[Zapf Dingbats]]

These fonts are sometimes called the ''base fourteen fonts''.<ref>{{cite web|url=http://desktoppub.about.com/od/glossary/g/base14fonts.htm|title=Desktop Publishing: Base 14 Fonts – Definition|last=Howard|first=Jacci|work=About.com Tech|archive-url=https://web.archive.org/web/20160614134144/http://desktoppub.about.com/od/glossary/g/base14fonts.htm|archive-date=June 14, 2016|url-status=dead}}</ref> These fonts, or suitable substitute fonts with the same metrics, should be available in most PDF readers, but they are not ''guaranteed'' to be available in the reader, and may only display correctly if the system has them installed.<ref name="aquarium">{{Cite web|url=http://www.planetpdf.com/planetpdf/pdfs/pdf2k/03e/merz_fontaquarium.pdf|title=The PDF Font Aquarium|last=Merz|first=Thomas|date=June 2003|url-status=usurped|archive-url=https://web.archive.org/web/20110718231502/http://www.planetpdf.com/planetpdf/pdfs/pdf2k/03e/merz_fontaquarium.pdf|archive-date=July 18, 2011}}</ref> Fonts may be substituted if they are not embedded in a PDF.

Within text strings, characters are shown using ''character codes'' (integers) that map to glyphs in the current font using an ''encoding''. There are several predefined encodings, including ''WinAnsi'', ''MacRoman'', and many encodings for East Asian languages and a font can have its own built-in encoding. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the [[Microsoft Windows|Windows]] and [[classic Mac OS|Macintosh]] operating systems, fonts using these encodings work equally well on any platform.) PDF can specify a predefined encoding to use, the font's built-in encoding or provide a lookup table of differences to a predefined or built-in encoding (not recommended with TrueType fonts).<ref name="pdf-ref-1.7" /> The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex.

For large fonts or fonts with non-standard glyphs, the special encodings ''Identity-H'' (for horizontal writing) and ''Identity-V'' (for vertical) are used. With such fonts, it is necessary to provide a ''ToUnicode'' table if semantic information about the characters is to be preserved.

A text document which is [[Image scanner|scanned]] to PDF without the text being recognised by [[optical character recognition]] (OCR) is an image, with no fonts or text properties.