Is this a bootable image

I downloaded the image from the link below but cannot get the pc to boot from this disc.I assumed that the ISO image will be a bootable one but I am not sure now.

www.linuxcnc.org/testing-stretch-rtpreempt/

Is there another ISO image that I can download. It must support the PlamaC installation.

Yes, they are bootable ISO's. I always suggest you burn them using win32diskimager on windows.
Plasmac is included in V2.8 and 2.9. That ISO is for 2.7 but you can upgrade in the usual manner.

The last time I installled Linuxcnc, I followed this method to get it runningon Linux mint
forum.linuxcnc.org/9-installing-linuxcnc...nd-easy-installation