Notable differences between the org.dita.pdf2 plugin in Open Toolkit 1.8.5 and 2.4
This is not a comprehensive list of changes by far. There are many changes (major and minor) that do not directly affect PDF plugin creation. Most of these changes have to do with various pre-processing steps that you are not likely to need to change.
To see the full release notes for each 2.x version of the DITA Open Toolkit, go to http://www.dita-ot.org, click the Docs menu, select the version, and then select Release Notes.
Separate plugins for each PDF renderer
Processing for all three PDF renderers (Antenna House, FOP, XEP) was previously combined into org.dita.pdf2. Processing unique to each renderer has been broken out into separate plugins: org.dita.pdf2.axf ...