Austin Z. has written pdf-writer, a tool to produce PDFs in Ruby.
Maybe you can use say, his file hello.rb, to adjust it’s output to
Arabic,
provided you have an
Arabic font available.
Maybe you also need to adjust the encoding, I think it’s ISO 8859-6 for
Arabic.
A more complicated alternative is to use the free and professional
layout
software
“latex”, which lets you generate postscript and pdf files. It has a
special
way
of generating fonts of its own. There is a special project Arabtex for
Arabic output
in latex.
But understanding how Latex works can be quite a lot of work for a
one-time
application 
Best regards
Axel