Solution: This is normal for portable workflows. Portable fonts are "volatile" by design. To fix this, keep the font file open in the background (the preview window) or use the PortableApps Font Loader plugin which creates a symlink.
Some people mistakenly believe that “portable font” means “I can give this font to all my 50 team members.” No. Each user must obtain their own copy legally. However, if you are a single user moving between your own devices, portability is legally fine.
Because JF Banumathi is a respected typeface, always download it from the official Junction Font repository or authorized Tamil font archives (e.g., Tamil Fonts by Junction). Look for the .ttf file. There is no separate “portable installer”—instead, you create portability yourself: jf banumathi font portable
If you don't want to carry a USB drive, make the document portable.
In Microsoft Word:
Caution: This increases file size (from 50KB to roughly 2-3MB), but it guarantees layout portability.
Since Windows does not natively support "double-click to run" for fonts permanently without installation, you must use one of the following methods to make it portable. Solution: This is normal for portable workflows
Use Portable Font Loader (free tool):