For invulnerability in this game, use the DOS utility DEBUG.
First backup your game to be edited, then type the following
from the dos prompt:
ren e:
aider.exe cheater.cht
debug e:\cheater.cht
e 1460 f8 c3
e 920 90 90 90
e 901 90 90 90
w
q
Then rename CHEATER.CHT back to its previous name.