For Base64 file encode/decode you can use built-in utillity certutil.exe (in c:\windows\system32):
[powershell]
certutil.exe -encode InFile OutFile
certutil.exe -decode InFile OutFile
[/powershell]
Note: because its for certificates … certutil add line „—–BEGIN CERTIFICATE—–“ (as first line of OutFile) and „—–END CERTIFICATE—–“ (as last line) when you encode some file