Publishing > PDF and Printed Manuals > CID mode for Unicode fonts

The CID Font Mode option in Configuration > Publishing Options > Adobe PDF > Font Embedding can reduce the size of your PDF for projects written in Unicode-based languages, particularly Asian languages. In addition to this it also improves the correct rendering of special Unicode characters in PDF.

When you set CID Font Mode to Unicode only the characters actually used in the font are embedded in the PDF file, in a special internal format.

This works correctly with most Asian languages. However, it may sometimes cause problems with western languages like Russian or other European languages with special characters.

How to use CID Font Mode

•	Western languages: Set CID Font Mode to CID Off for all normal western languages like English and most other Western European languages. You should also turn CID off for Eastern European languages like Russian, Czech, Polish and so on.

•	Asian languages: Set CID Font Mode to Unicode for all Asian languages based on Unicode fonts.

•	Special Unicode characters: If you use special Unicode characters in your project you may need to activate Unicode mode to get the characters to display correctly. Please check the rest of your output carefully for correct rendering when you do this.

Although Help & Manual can generate PDFs from projects written in Unicode-based languages, the Adobe PDF format does not actually support Unicode directly. This is because PDF is a universal format designed to be displayed on any computer running any operating system. If PDF files were encoded with Unicode they would not display on older operating systems like Windows 98 and Windows NT that have no Unicode support.

PDF files gets around this problem by using a different encoding internally that can map and represent all the Unicode characters. PDF currently supports two internal encoding formats for Unicode: double-byte characters (which are often mistakenly confused with Unicode) and "character identity definition" or CID.

CID Font Mode: Unicode

When you set CID Font Mode to Unicode the PDF engine does not embed the entire font. Instead, it only embeds the characters that are actually used, which are stored in a special internal format. This works well for most Asian languages and will usually provide a significant reduction in PDF file size.

CID Font Mode: CID Off

When CID Font Mode is set to CID Off Unicode character codes are exported in double-byte format and fonts are generally embedded in the PDF (except for common fonts like Arial). This works well with western languages but it does not work with Asian languages and other languages based on Unicode.