Glyph and Ligature problem with Acrobat 8
20 Jan 2009
by: Redlin
Redlin has experienced some problems with glyphs and ligatures with documents produced in Indesign and outputted using Acrobat 8 - further details are available below - alternatively, please contact sales at Redlin for further information.
Glyphs and Ligatures
Redlin has been supplied press ready PDF (Portable Document Format) files from at least four independent sources. All the supplied pdfs were generated from Indesign using the export facility. With all files, we have experienced some degree of problems with glyphs and ligatures at output stage.
What are glyphs and ligatures?
Glyphs are a visual representation of a 'letter', 'character' or 'symbol' in a specific typeface/font.
A Ligature is the joining of two or more characters to produce a single glyph. Most common ligatures are fi ffi ff fl ffl.
After extensive investigation, we have discovered that Acrobat 8 does not support Ligatures and will display blanks in their place eg. 'flexible' becomes ' exible'. When creating the PDF file, no warning is produced that this has occurred. It is believed that earlier versions of Acrobat, version 7 and below do not experience this problem.
The problem so far has only manifest itself with Indesign. It would appear to be a combination/conflict between the export setting used, the fonts and the transparency filters within the source document.
What can be done?
1. Convert all type to outlines.
Prior to exporting file to pdf, convert all the fonts to outline, negating the potential problem. The type is now a vectorized image which is not effected by glyphs and ligatures. The drawback to this is that it is advised to keep a copy of the file without converting type to outlines in case of any alterations that maybe required. Once converted these changes cannot be easily made.
2. Export the file on an alternative setting.
When exporting the file select:
Standard: PDF/X 1a-2001 Compatibility: Acrobat 4 version 1.3. This setting enables you to flatten transparency at pdf creation stage.
The setting to avoid when exporting the file is Standard: PDF/X 1a-2001 or above Compatibility: Acrobat 5 version 1:4 or above. This setting maintains transparency at pdf creation stage, leading to potential problems.
The important thing here appears to be the compatibility details. Any setting higher than Acrobat 4 Version 1.3 does not allow the facility to flatten at pdf creation stage. It is this relationship with Acrobat 8, the transparency and fonts that cause the ligature problem at outputting stage.
For a printable version of the warning, please click on the following link:
Redlin Pre-Press Warning.pdf