In spite of the abundance of documentation on how to use font files, and how to create documents with text in different languages, people are still asking the same question in many different variations. That's why this separate entry was made, using a different phrasing of the same question that was answered many times before.
The reason why characters are missing is simple: you are not providing a font that can render those characters. How to solve this problem? That's explained in Chapter 6, and in the answer to the question Which languages are supported in pdfHTML?