Icacls "C:\Test\test.txt" /grant Everyone:f
should be:
icacls c:\test\test.ext /grant Everyone:(F)
or
icacls \\localhost\c$\test\test.ext /grant Everyone:(F)
if the user or group name has a space in it, include it in quotes such as "Domain Admins" or "Enterprise Admins"
icacls \\localhost\c$\test\test.ext /grant "Enterprise Admins":(F)