Hindi fonts not available in Invoice

I have a book publication webiste, we have books in many languages and most of the titles are in english , but some titles are in hindi, when an order placed for the hindi books , the title is not visible and replaced by special chartaters. please help to fix it, or add hindi fonts in the invoice please. The screen shot is attached in above link. you can see in place of hindi fonts , their are special characters.please help me out asap.

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