How Manuscripts Get into PubMed Central (PMC):
Method A: Journals automatically post NIH-supported manuscripts directly to PubMed Central (PMC).
Method B: Authors make special arrangements for journals/publishers to post their manuscripts directly to PMC.
Method C: Authors of their designee submits manuscripts to the NIH Manuscript Submission System (NIHMS).
Method D: Publishers submit manuscripts to the NIH Manuscript Submission System (NIHMS).
Source Reference: https://publicaccess.nih.gov/submit_process.htm