This format can...
read and write waypoints
Magellan NAV Companion for Palm/OS is not really designed for this sort of use, but its file format is supported and with a little bit of patience you can both read and write NAV Companion waypoints. This conversion is based on partially incomplete reverse-engineering of the record format, so it may not work with all versions of NAV Companion. It has been tested with version 2.10 and 3.20.
Translating NAV Companion waypoints to another format is as easy as with any other format. Just find the Companion_Waypoints database in your palm backup directory and use it as the input file.
When translating waypoints back to NAV Companion, though, you need to jump through some hoops:
First, you must merge any waypoints that already exist in the database in your Palm Backup directory with the ones you are adding; failure to do so will result in only the new points being available in NAV Companion, even if you give the new database a different name (it will overwrite the old database, even in your backup directory. That's a feature of PalmOS, not of NAV Companion.)
To merge the databases, use a command line like the following:
gpsbabel -i magnav -f Companion_Waypoints.PDB -i geo -f geocaching.loc -o magnav -F merged.pdb
Second, you must use the installer to install your new PDB file. Don't make the mistake of copying it over the existing Companion_Waypoints.PDB file; the one on the handheld will overwrite it rather than merging with it.
Finally, because NAV Companion is not designed to work with desktop applications, you must tell NAV Companion that its waypoints database has changed out from under it. One way to do this is to go to the waypoints screen and attempt to scroll; that will force it to reread the database and fix the record pointers that it keeps on the heap.