Sorry I'm seeing this so late.

Pmd already has support to analyze pom files https://pmd.github.io/latest/pmd_rules_pom.html

So I'm unsure what you are trying to achieve.

You are probably suffering from this problem: #1540
pom.xml files have the extension "xml" and not "pom"... but the extension "xml" is already used by the general xml language module.

Since PMD 6.37.0 there is a workaround with --force-language and the following execution indeed works:

pmd-bin-6.50.0/bin/run.sh pmd -d pom.xml -f text -R category/pom/errorprone.xml/ProjectVersionAsDependencyVersion --force-language pom

You'll need to mention the pom.xml files explicitly (just giving a directory doesn't work as PMD would search for *.pom files...) and add the "--force-language pom" option.