What is a file extension?

OTF File - What is an .otf file and how do I open it?

The complete list of font formats and their use — FontsArena

Logo file extensions explained the easy way. — Signs On Time

Rename a File Extension Easily on Phone, PC or Mac Computers

windows 7 - Use File TypesMan to change extension setting, but it show this file type may affect the following extensions - Stack Overflow

FontARA Font Changer extension - Opera add-ons

Finding and removing Type 1 fonts on Windows – Extensis

How to Install Fonts in All Versions of Windows - Simple Help

File Extensions Associations

CAD File Extensions - TransMagic