ngoldie wrote:..how to open an old Archicad .pln file after downloading the 6.5 file converter..
I need to convert it to Archicad 20...
I think your OSX must be at least 10.9, and probably even newer?
Sorry to say, but the procedure is a little bit difficult with a Mac nowadays.
ArchiCAD 6.5 converter does not work in your Mac. Neither does ArchiCAD 9 converter. You would need Snow Leopard (OSX 10.6) to run Rosetta environment (it is a PPC emulator software) to run the above mentioned converters (AC6.5 and AC9). AC 10 converter works with intel Macs and newer OS X versions, but it does not open the oldest pln-files.
If your old files are of version 6 or even older, you are out of luck with your machine, because you would need snow leopard to open those files first, and then you could go on further.
You might have a friend with a WinPC. A PC probably can run all the converters available for windows OS versions. I am not sure.
What opens which versions:
File versions matrix
This is why I still have an old iMac 24" with OSX 10.6 Snow Leopard available. And we still do have some ArchiCAD 3.42 files on floppy disks somewhere.