Inject my a code into all files?

So basically I'm designing an antivirus that injects into all files to make sure a virus doesn't remove the antivirus.

My question is, is this possible? If so how would I go about doing it? Any help is appreciated.

That sounds very much like what a virus would do, and is probably a case of the cure being worse than the disease.

We don't help with malicious code, which that would be.