Always prefer Unicode fonts for new documents. They are future-proof and your text will not break when shared.
Typing in Tamil in contemporary and ancient scripts - The Digital Orientalist tamil font in ms word
Whether you are writing a letter, designing a poster, or typing a school assignment in Tamil, Microsoft Word fully supports the language. However, getting the fonts to appear and type correctly can be confusing due to two different encoding systems. This guide will clear that up. Always prefer Unicode fonts for new documents