Document doc = ConvertUtil.GetNewEngineDocument();
doc.loadFromFile(input);
HandleDocumentSubstitutionWarnings substitutionWarningHandler = new HandleDocumentSubstitutionWarnings();
doc.setWarningCallback(substitutionWarningHandler);
doc.saveToFile(output_1);
StringBuilder sb = new StringBuilder();
Iterator iterator = substitutionWarningHandler.FontWarnings.iterator();
while(iterator.hasNext()){
    System.out.println(((WarningInfo)iterator.next()).getDescription());
}
String s = substitutionWarningHandler.FontWarnings.get(0).getDescription();
WarningSource warningSource = substitutionWarningHandler.FontWarnings.get(0).getSource();
substitutionWarningHandler.FontWarnings.clear(); 
class HandleDocumentSubstitutionWarnings implements IWarningCallback
{
    public void warning(WarningInfo info) {
        if(info.getWarningType() == WarningType.Font_Substitution)
            FontWarnings.warning(info);
    }
    public WarningInfoCollection FontWarnings = new WarningInfoCollection();
}