As a pro I often have to install software on customers machines (individuals, not companies).
One of my first choices is OOo 2 (+ VLC & XnView) but earlier this month I had to use the older version (1.15) on a slow computer.
Now I got a call from the gentleman, stating that the .THM extension was overtaken by OOo for the configuration files.
He cannot anymore previsualize or view his MOVXXXX.THM movies with the said extension.

I Googled this extension, but no clue on how to rebuild Windows original viewing - as neither he nor I know what the original file was.

Would anyone here be able to give me a lead?
Thank you.