Export OMF From Pro Tools to Reaper
Pro Tools can export a session as an OMF file, which Reaper can then open once it's converted into a native RPP project.
If your session lives in Pro Tools and you (or a collaborator) need to keep working on it in Reaper, OMF is the bridge between the two: Pro Tools can export one, even though it can't produce a Reaper project directly.
In Pro Tools, select the tracks you want to bring across, then use File > Export > Selected Tracks as New AAF/OMF and choose OMF as the format. Pro Tools exports the audio only — video isn't included, so if the session has picture, that stays separate.
Once you have the .omf file, it can't be opened in Reaper as-is — Reaper doesn't read OMF natively.
You can convert your OMF file for free here.
A 2-minute walkthrough of how to open an OMF file in Reaper, from start to finish.
Everything you need to know about OMF files and Reaper: how to open an OMF in Reaper, how OMF exports work (embedded vs. non-embedded), what they contain, what's missing, and what used to break before this converter existed.