You'll need to either check out the source code or download the latest source release. Assuming you've got the latest source release, unzip it to a directory:
[tom@hal building]$ ls -l
total 5716
-rw-rw-r-- 1 tom tom 5837216 Jul 17 13:09 pmd-src-5.0.zip
[tom@hal building]$ unzip -q pmd-src-5.0.zip
[tom@hal building]$
Now cd down into the pmd directory:
[tom@hal building]$ cd pmd-5.0
[tom@hal bin]$ ls -l | grep build.xml
-rw-rw-r-- 1 tom tom 5736 Jun 19 15:36 build.xml
[tom@hal bin]$
There's our Ant build file... let's compile!
[tom@hal bin]$ ant compile
Buildfile: build.xml
compile:
[javac] Compiling 509 source files to /home/tom/data/pmd/pmd/build
BUILD SUCCESSFUL
Total time: 6 seconds
[tom@hal bin]$
Notes:
A paucity of detail, I'm sure you'd agree. If you think this document can be improved, please post here and let me know how. Thanks!