How to make a newer Premiere project open in an older version
A collaborator is on an older Premiere, but your .prproj was saved in a newer one. That is the classic downgrade case. The point is not renaming the file; it is removing what the older app cannot read.
Start with the recipient’s installed version
Pick the target based on the receiving machine, not yours. Ask them to check the version number in About Premiere Pro, then choose CS6, a CC release, or the year-based version that matches.
Downgrade the project, not the media package
The conversion works on the .prproj file itself. Video, images and audio are not rewritten or transcoded. You still need to keep the media folders organised, or the older app may open the project with files offline.
Stay close to the source when possible
If the collaborator is only one or two releases behind, choose the closest target. The further back you go, the more newer features the target cannot represent.
Open the result before delivery
After downloading the converted file, open it in the target Premiere version. A real check means the project opens, the timeline is intact, and media can be relinked.