I already filled my tax return but just received my 1095-c (proof of health insurance ) can I add this document or is it too late ?

great news for you. this form does not get entered on your return.  there is no place to enter it on the federal return. if your state has an income tax it might require some info about health insurance coverage. those questions will only come up when you get to the state. many states do not have any health insurance questions. 

You don't include From 1095-C on the return. It is for your information only.

Ok,Thank you. I just remember seeing something that said while I didn’t need to show proof of Health insurance this year that it could hold the return up.