Difference between full embedded fonts and embedded subset

What fonts are supported in the PDF format?

The PDF file format supports the use of the following font formats:

- TrueType
- Type 1
- Type 3
- Composite fonts (Type 0): both Type 1 (CIDFontType0) and TrueType (CIDFontType2) are supported.
- OpenType: From PDF 1.6 onwards, OpenType fonts can be stored directly in PDF files. In prior releases OpenType fonts are embedded as either Type 1 or TrueType fonts. The ability to embed OpenType directly was added for the forms capabilities of PDF, it offers no immediate advantage  for prepress users.

What is the difference between Embedded fonts and Subset Embedded fonts?
By preference any fonts that are used in a layout are also included in the PDF file itself. This makes sure that the file can be viewed and printed as it was created by the designer. There are two mechanisms to include fonts in a PDF:

- Embedding: A full copy of the entire character set of a font is stored in the PDF.
- Subsetting: Only those characters that are actually used in the lay-out are stored in the PDF. If the “$” character doesn’t appear anywhere in the text, that character is not included in the font. This means that PDF files with subsetted fonts are smaller than PDF files with embedded fonts. For subsetted fonts, the font name is preceded by 6 random characters and a plus sign.

If certain fonts are missing from the PDF file, Adobe Acrobat and Adobe Reader will automatically try to emulate the missing font by using one of the Multiple Master fonts that are built into these programs. This way, the document will not be represented exactly as the designer wanted it to, but at least the text won’t reflow. The Multiple Master fonts that are used for this are:

- Adobe Serif MM
- Adobe Sans MM

Another important aspect of font handling is the encoding. This refers to the mapping of a character code to a particular glyph (character shape) description. Each font in a PDF uses a specific type of encoding, either a standard one or a custom one. The following types of encoding are supported by the PDF file format:

- StandardEncoding
- WinAnsiEncoding
- MacRomanEncoding
- MacExpertEncoding
- A custom encoding can be used by defining a ‘Differences Array’.

How to embed fonts

Some applications such as Adobe InDesing automatically embed all fonts when pages are exported to PDF.

Acrobat Distiller offers an option to automatically add missing fonts to PostScript files it has to process. In the font locations menu, the user can define several folders that have to be searched for fonts that are missing in the PostScript file. Distiller only needs the printer fonts, it does not need the screen fonts.
Fonts that are not necessarily included in PDF files

Older versions of Adobe Acrobat (Acrobat 3.x and earlier) will never embed the following 14 fonts t in a PDF file:

- Courier, Courier-Bold, Courier-Oblique & Courier-BoldOblique
- Times-Roman , Times-Bold , Times-Italic & Times-BoldItalic
- Helvetica, Helvetica-Bold, Helvetica-Oblique & Helvetica-BoldOblique
- Symbol
- ZapfDingbats.

These fonts, excluding ZapfDingbats, are called the Base 13 fonts.

From Acrobat 4.x onwards, thereis no problem embedding the above 14 fonts. In fact it is a good idea to actually always embed these fonts as well. Instead we got another restriction: if the licensing policy of a TrueType forbids the font to be included in a file, Distiller 4 and later will respect this restriction and will not embed the font.

How to subset fonts

It is possible to only include those characters of a font that are actually used in the publication. This technique is called ‘font subsetting’.

Usually you can specify that font subsetting needs to be used as soon as a certain percentage of the character set of a font is used. Below is the option that is shown in Adobe InDesign CS4. A similar ‘Subset fonts below XX %’ parameter is available in Acrobat Distiller.



There are 2 advantages to subsetting fonts

- It reduces the size of a PDF file and can be handy if file size is really crucial, for instance for PDF files that will be downloaded from the web.

- RIPs will always use a subsetted font, even if the full font is already available on the RIP. This way text reflows caused by differences between fonts can be avoided.

There are two disadvantages to subsetting fonts:

- If you want to edit text in certain PDF Editors and the character you need is not included in the subset, it cannot be used in the correction. Acrobat itself does not suffer from this. It only uses the system fonts for editing.

- Merging two files that contain a different subset of the same font can lead to missing or swapped characters. Older PDF applications can suffer from this. Most of these bugs have been fixed in more recent versions.