Tfpdf与阿拉伯字符

I am using Tfpdf to create a PDF file. This PDF file contains both Arabic word and English word. My problem is with the Arabic word.

The Arabic word is written from right to left.

The problem is I have a result with separate characters and the characters are written from left to right which make the word unreadable .

This photo explain what I am trying to say. The word in Arabic should be مرحبا بكم.

How can I solve this problem?