assuming you meant DMG (since the F key is besides the G key on a QWERTY keyboard I will take DMF to be a typo) then yes, it is a mac format. They are disc images (kinda like ISOs). It is also the default format for distributing binary's for Mac. Was there something specific that you wanted to do with a DMG file?
my bad it was .dmg ya i jsut downloaded a program fro my pc and didnt find out that it was .dmg (or didnt pay enough attention ) untill after i downloaded it i assume there is no way to convert it?