Bonjour Christian - I don't believe that Euclid has been developed for quite some time now so it will likely be quite difficult to find other software that can read and write its native file format (which I guess is your .XDB? I am not familiar with XDB myself).

According to here: http://en.wikipedia.org/wiki/Euclid_%28computer_program%29 it says that BRL-CAD is able to import from the Euclid file format, so maybe there is some possibility to use BRL-CAD as a way to transfer it to STEP or something.

- Michael