Your ANT file is not *quite* a copy of what's in the book. 🙂 You have the line
which calls the build file in your plugin. If you've followed the instructions in the second edition of the book (which is meant for DITA OT 2.x), then you do not have a build file in your plugin.
You want to copy the line exactly as it is in the example in the "Create an ANT build file/Reality check" topic, which is:
This calls the main build file in the OT itself, which kicks off a whole pipeline of things that must happen for a successful build.
That said, if you are using this ANT file as-is, then you need to be building a ditamap named WidgetUserGuide.ditamap, which lives at C:\Widget, and you need to be outputting to C:\Widget\output\pdf, and the transtype defined for your custom PDF plugin must be "custpdf." In other words, you have to be exactly matching my example in all respects for this to work.
Also, if you can, I would recommend updating from OT 2.0 to OT 2.5.4. The version you have is an early 2.0 version and likely to include a lot of bugs that have been fixed in later versions. OT 2.5.4 is the last 2.x version and is quite robust and widely used.