Assuming you can still run whatever version of TNA you have, best bet would probably be to load the data into TNA in the normal manner, export to .gpx, then load that into Basecamp. And no, I no longer remember the details. I’ll see if I still have a running version, but I’m pretty sure not. At some point, it failed to install on the latest version of Windows, I think.
I find mixed info online regarding TNA10 compatibility with Win10.
There is a manual available here http://static.garmin.com/pumac/TopoNA10Manual.pdf. But if you have a running version, you don’t need that. Note that it does include instructions for exporting to .gpx.
I also checked ExpertGPS, which is also limited to .an1.
Inexplicably, GSAK will export to DeLorme Format, but will not import. It makes no distinction between format versions. Pretty sure that GSAK uses GPSBabel under the hood.
Anyhow, advice remains the same - use your copy of TNA to export to .gpx.
