DacEasy (v9 and v10 to 14 and Utilities) when I last used it over 2 decades ago was using dBASE (.DBF) files. It should be trivial to export them out into Excel / CSV files before importing them into MySQL directly. DacEasy last used BTRIEVE database for DOS that is akin to MySQL's ISAM (Indexed Sequential Access Method) DB Engine.
The manual for DacEasy v14 is available here and it's list of files and what they are for is listed here.
Commercial products to convert Btrieve DB to MySQL DB are:
Mertech Btrieve to MySQL
FullConvert Enterprise - abandoned / unsupported / lost on the web
Nelson Software Tools
BTrieve itself is now Pervasive SQL (PSQL) - MySQL Discussion thread for conversion.
DacEasy is now part of Sage and they do not generate Activation keys for these old versions when you need to re-install. Provide feedback if this works.
If you are interested in still using DacEasy, it can be setup in a DOS emulator and run on the newer OSes along with an LPT2USB Driver for them.
Capturing LPT1 is also possible.
FreeDOS supports USB Printers.
You can also run DacEasy in a DOS VirtualBox / VMWare Player / QEMU Emulator.
DOSBox too can be used.