The National Institutes of Health (NIH) developed the NIH Manuscript Submission (NIHMS) system to facilitate the submission of peer-reviewed manuscripts for inclusion in PubMed Central (PMC) in support of the NIH Public Access Policy. Since its inception in 2005, NIHMS has expanded to support the public access policies of other organizations and government agencies. The NIHMS system allows users, such as authors, principal investigators, and publishers to supply material for conversion to XML documents in a format that can be ingested by PMC. Depositing a manuscript in NIHMS for inclusion in PMC is a multi-step process, requiring an author to approve the deposited files and associated funding before conversion and the PMC-ready version after conversion.(Source: About NIHMS)
There are a variety of log-in options based on researcher affiliation.
"Overview of NIHMS submission process" Retrieved from NIHMS