Use this method to subset a previously embedded font.
Many PDF producers are not efficient at subsetting fonts.
Subsetting previously embedded fonts can be a time consuming
operation but can also result in a significant reduction in file
If you provide a character set string then this is a relatively
fast operation. However if you do not pass a character set then one
has to be constructed and to do this it is necessary to analyze the
entire document to determine what characters are being used. In
this case if a call to Catalog.AnalyzeContent
has not already been made then one will be triggered.
This call will subset embedded TrueType and CFF fonts (Compact
Font Format). If the font is referenced or if the font is not one
of these types then this function will return false.