connect to hdmi/PC

if you mean to act as a monitor then not out of the box but you can take a look at

Luna Display | Turn your Mac or iPad into a second display (astropad.com)

and or

Duet - Remote Desktop, Second Display, Drawing Tablet, and More (duetdisplay.com)

but mind you, the imac would be using the same kind of power as if you were using it normally so your electricity usage would be way higher than if you just used a monitor with your pc