The file used to provide information to the CPU & GPU while playing that game. So the “ISDone.dll is missing” error message frequently arises during the installation of computer games gets failed. The "ISDone.dll" & "Unarc.dll" are the files that, like all the other "DLL" files, situated at the System32 folder on 32-bit computer systems whereas in the SysWOW64 folder for 64 bit PC.