bioRxiv converts PDFs to full-text already. They're right there on the bioRxiv web site—just click the "Full text" tab. For example, our most recent bioRxiv preprint:

https://www.biorxiv.org/content/10.1101/2022.01.07.475366v1....

If you want to do URL munging instead of using the UI, just add `.full` to the end of the URL ;)

This doesn't require that the manuscript be submitted in any particular format either. There are humans involved in making sure the full text formatting from PDF is good.