FINISHPAGERUN - launching Acrobat Reader ...?

Is there an easy way of launching Acrobat Reader [filename] from the FINSIHPAGE_RUN
or do I have to find out what version is installed etc etc?

You should use ExecShell in an MUI_FINISHPAGE_RUN_FUNCTION function.
See

Launch your pdf in the LaunchLink function instead of .lnk

great , works perfectly, thanks