There are several ways to open a font file.
Open fonts already installed on your system
To open an installed font file select Open from the File menu and choose Installed Font option.
Open any font that is available
From the File menu, select Open and choose Font File option to open a font through Windows default open dialog box.
Drag and drop a font file
Another way to open a font, is to drag a font file from Windows Explorer and drop it into FontCreator.
Explorer Context Menu
You can also open a font from My Computer or Windows Explorer context menus. Select one or more font files in a Windows Explorer window, then right click any of the selected files and choose Open with FontCreator from the context menu
Reopen a font file
To open a font that you've used recently, choose Reopen from the File menu to display the names of the last ten used fonts. Click on the font you want to use.
Warning: If you want to open fonts that are located in Windows fonts folder you should use the Installed Fonts command (or drag and drop), because this folder is marked (by Windows) to be a special folder and therefore behaves differently (e.g. it shows font names instead of file names).
Warning: Really large fonts can only be loaded when your system has enough internal memory.