As of the 2017 version, all files can now read on both the Mac and the PC version of the software.
If you are using Mac, your files have always been .rp8 files.
If you are switching from PC to Mac, you will need to convert your files before they can be read in the 2017 and forward version OR on the Mac version.
To convert files, go to the file dropdown and select "Convert old .rp7 files".
You can elect to convert one file at a time or a whole folder at a time.