how to check file extension

A Simple Guide to Font File Types

Different Font File Types Explained (OTF, TTF, WOFF)

Understanding font file formats(ttf, otf, woff, etc) - Snapfont

How to turn on hidden filename extensions in Windows

What is a file extension?

Error Creating Text Style '(text style name)': Font File '(font name)' Not Installed (Using a Land F/X Tool, or Placing Text)

RTF File - What is an .rtf file and how do I open it?

Which font tables are required when embedding an OpenType font into a PDF file? - Stack Overflow

File Extensions Associations

windows 7 - Where are the physical font files stored? - Super User