Upload a Premiere Project (.prproj) file and this tool will instantly convert it to be openable in any older version of Premiere.
Your file will automatically download upon clicking Convert.
This tool resets the version number, so when you open it in Premiere you will be asked to resave as the current version.
Some effects and filters may be missing after re-opening.
A Premiere project (.prproj) file is basically an xml file wrapped up in gzip compression. One of the nodes contains a version number corresponding to the version of Premiere which created it. Premiere checks this when opening a file and refuses to open anything with a lower version number, even when the project is basically compatible: "This project was saved in a newer version of Adobe Premiere Pro and cannot be opened in this version."
This tool simply changes that version number to '1' and creates a gzip compressed file which Premiere can read. You can perform the same process yourself manually, as described here, however this tool makes it simple.
Because this is a cheat, some filters and effects may be lost when converting. The most notable difference is the 'Type' tool which was introduced in April 2017 to replace the titles feature. There is no way to replicate this in an older version.