== Themes

The layout and styling of the PDF is driven by a YAML configuration file. To
learn how the theming system works and how to create and apply custom themes,
refer to the _Asciidoctor PDF_ Theme Guide. You can use
the built-in theme files, which you can find in the *data/themes* directory,
as examples.

=== Support for Non-Latin Languages

_Asciidoctor_ can process the full range of characters in the UTF-8 character
set. That means you can write your document in any language, save the file
with UTF-8 encoding, and expect _Asciidoctor_ to convert the text properly.
However, you may notice that certain characters for certain languages, such
as Chinese, are missing in the PDF. Read on to find out why and how to
address it.

If you're writing in a non-Latin language, you need to use a dedicated theme
that provides the necessary fonts. For example, to produce a PDF from a
document written in a CJK language such as Chinese, you need to use a CJK
theme. You can get such a theme by installing the `asciidoctor-pdf-cjk-kai_gen_gothic`
gem. See the {uri-asciidoctor-pdf-cjk-kai_gen_gothic}[asciidoctor-pdf-cjk-kai_gen_gothic, {browser-window--new}]
project for detailed instructions.

Using a dedicated theme is necessary because PDF is a "`bring your own font`"
kind of system. In other words, the font you provide must provide glyphs for
all the characters. There's no one font that supports all the worlds languages
(though some, like Noto Serif, certainly come close). Even if there were such
a font, bundling that font with the main gem would make the package enormous.
It would also severely limit the style choices in the default theme, which
targets Latin-based languages.

Therefore, we're taking the strategy of creating separate dedicated theme
gems that target each language family, such as CJK. The base theme for CJK
languages is provided by the {uri-asciidoctor-pdf-cjk}[asciidoctro-pdf-cjk, {browser-window--new}]
project and a concrete implementation provided by the
{uri-asciidoctor-pdf-cjk-kai_gen_gothic}[asciidoctor-pdf-cjk-kai_gen_gothic, {browser-window--new}]
project that's based on the kai_gen_gothic font. Of course, you're free to
follow this model and create your own theme gem that uses fonts of your choice.