How to generate a PDF in thai language

Hi
I create form in form builder.
I can type thai language in form and save
but when I generated PDF, Thai language words is empty space.

example
If I type in form
expert11 123 วิทกานต์

It remain in pdf
expert11 123

word วิทกานต์ is gone.

how to find out
1) modify class in orbeon.jar.
What class I should modify?
2) change font in config properties.
how to change?

Anyone help? :)

Please help me