But I cant. It is saved as a MAC file and needs converting to PC. The file name would not be:
._unhealthy_or_healthy_layered.psd
but
unhealthy_or_healthy_layered.psd
I get a wrong format error on my PC when trying to open it.
The file you have is the resource fork file rather than the data fork. Did you receive the file in a .zip archive? There should be a data fork in the package as well, named, as you wrote, unhealthy_or_healthy_layered.psd. See this discussion.