I came across this recent thread which seems to confirm that there is no direct way to use TM25 ray files in Zemax. The suggestion there is to go to the source of the ray file, and get a different format, which can be converted using a third party tool to a format Zemax can use.
In my case, the source of the TM25 files does not provide any other format, so this is not an option for me.
Is there anything else I might try? I don't have access to the IES TM25 spec, so converting the files myself is not really an option—and writing my own binary file parser is not something I would do with confidence or enthusiasm.
Maybe someone at Zemax would like to take a stab at this? A quick-and-dirty, completely unsupported Python script would be a huge help. I'm not sure how many different types of information are contained in a TM25 file, but ray origins, directions, and intensities would be enough in my case.
I've been in touch with Sandrine, our engineer from that previous thread. She'll be discussing this topic shortly with our Product team. I hope then we can get a more up-to-date answer to you and to all of our users who are looking at TM25.
Thanks Kevin. I ended up finding a TM25-processing C++ class on Github.