I have a pinhole in the back coil that I accidentally punctured and all the freon leaked out. The hole is no bigger than a pinhole.

Id like to know if the pin hole can be patched, and freon replaced? Or is the entire refrigerator now useless due to this tiny pin size hole?

I can't afford to buy a new fridge if it needs to be replaced.

Thank you so much

Likely can be repaired. Depends on where and how easy it is to get a torch in there.
Service valves will likely have to be added, vacuumed doen, leak tested, and if the frige is old and uses R-12. R-12 is getting expensive.

If it's in an aluminum piece instead of copper, I don't knpw.

Difficuilt to repair evaporator. Try Red expoxy. If unit is older, may be better off replacing