I've just downloaded and installed perl-Convert-TNEF. This was recommeded for reading winmail.dat files. I'm not a perl user. No man page was installed, nor a binary/command.

How do I use this module?

Later ...

Wow, this is turning into an unexpectedly complicated project. I've moved on from the perl module and I've downloaded tnef from github and built it. I've tried:
and absolutely nothing happens. Any ideas? The winmail.dat files I'm using is: http://www.novatec-inc.com/pub/winmail.dat if you want to look at it, which is an attachment sent to my by a friend and Windows/Outlook user and does contain text (I've dumped) it. In fact, I can read it with lynx as it is essentially an html attachment of the actual message.

Why does tnef do nothing?

The Perl module seems to be a library you can use in a Perl program, but not as a standalone program.

I can't tell why tnef does nothing, but if you add the --debug option, you get a lot of output, including some data that seems to come from the winmail.dat file:
EDIT: A strings winmail.dat reveals the HTML and more message content.

EDIT2: To communicate with the author of the tnef program, I suggest you create an issue at https://github.com/verdammelt/tnef. Looking at the timestamps in the Git repository, the project seems to be active. Perhaps the author would be grateful for TNEF files that don't get converted.

So the Perl thing is a module (like a library) & howto with examples is here https://metacpan.org/pod/Convert::TNEF .
If you need further assistance, try the gurus at perlmonks.org

not sure if this would help in your scenario, but you can also just use the tnef command to extract the needed files.