When using FOP for generating PDF documents using a custom font you need to provide what is called a metrics file
the metrics file contains the measurements information for the designated font like the height of the characters and so on
to create this file you can use the TTFReader tool provided with FOP as follows
Code:
java -cp build\fop.jar;lib\avalon-framework.jar;lib\commons-logging.jar;lib\commons-io.jar
org.apache.fop.fonts.apps.TTFReader [options]
C:\myfonts\cmr10.ttf ttfcm.xml
Make sure that you have java installed on your machine first
run this command from the root of the FOP folder(Where you expanded the FOP zip file)
ttfcm.xml is the generated metrics file