You can publish in a journal that deposits all final published articles in PMC without author involvement. Some journals automatically deposit all NIH-funded final published articles in PMC, to be made available within 12 months of publication, without author involvement.
There is no fee for this service. If an author publishes in one of these journals, no further action is required except that the author is responsible for citing the PMCID number in future NIH applications, proposals and progress reports.