I became very curious about this, and from what I've read it seems that if you are using the standard English qwerty keyboard, you need a special keyboard layout to type in Arabic text because the English alphabet has fewer letters than the Arabic alphabet.
I'm guessing this is some kind of software, but that's about all I can glean from what I've read. This isn't really an issue with Painter, but I hope the information will be helpful to you. It seems very complicated to me.
If you have a graphics tablet, you might find it easier to use one of the Painter pens to write/draw your Arabic characters by hand into your document.
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DAA InstructorIntroduction to Painter 12: Part 1Introduction to Painter 12:Part 2Introduction to Painter 12:Part 3
On Hiatus:Creative Collage at DAA