“Referenced” describes any font that is not embedded in the PDF document. Referenced fonts can be identified in a PDF file through the Fonts tab of the Document Properties dialog – any referenced fonts will not have the text “(Embedded)” or “(Embedded Subset)” in that tab’s font list. Rendering PDF text for a referenced font requires a matching, locally-installed system font or a substitute.
The ideal rendering solution is to match each referenced font, by name, to a font installed on the local system. This will yield the highest-quality text output for the PDF document. Without a matching font, a similar substitute font is the next best option
For Latin alphabet text there is always (?) some font that can be used. Most operating systems include fonts with Latin characters and PDF rendering software is suggested (PDF spec, §5.5.1) to have “14 Standard” Latin fonts available.
Finding CJK fonts to render a document with referenced fonts can be more challenging. Current versions of Microsoft Windows and Apple OS-X operating systems include CJK fonts – these, when found, will be used by Qoppa’s PDF library to render CJK text.
Linux operating systems – especially server installations – often do not include CJK fonts. So, CJK fonts must be separately found, installed and configured in order for Qoppa’s PDF library to correctly render CJK text on web pages.
If CJK fonts are not available then any page containing these fonts will not be rendered by Qoppa’s PDF library – instead an error page will be shown with a message like “Unknown CID font: Adobe::GB1”. (“GB1” indicates that a Traditional Chinese font was not found – there are similar messages for the other CJK language texts: “Japan1” (Japanese), “CNS1” (Simplified Chinese), “Korea1” (Korean)).