The MacTeX is perfect for Mac OS X to enable pdf generation on R with the power of TeX. The following URLs are the official site and a how-to for Japanese language.
Because the R help should be written in English, no dditional settings (such as Japanese fonts) are required.
Just install the downloaded package MacTeX.pkg. And after that, running R CMD check ./HelloWorld_1.0.tar.gz will generate a pdf help file.
R CMD runs as same as on Windows OS shown at the previous post, but an important difference is the current directory is used to read and write package files on Mac OS X, though the temporary directory is used on Windows OS.