Private Declare Function AddFontResource Lib "gdi32" Alias "AddFontResourceA" ( _
  ByVal lpFileName As String) As Long
 
Function InstallFont(strFilename As String) As Boolean
Dim nReturn As Long
nReturn = AddFontResource(strFilename)
InstallFont = CBool(nReturn)
End Function

FileCopy "C:\Temp\TempFont.ttf", "C:\Windows\Fonts\Odins_Runen.ttf"
If InstallFont("C:\Windows\Fonts\Odins_Runen.ttf") = False then Msgbox _
  "Fehler", vbCritical