You have build your program as a derivative of existing open source software component, licensed to you under the EUPL.
In case of distribution, your program must be licensed by you under the EUPL.
In case your program can also be considered as a "Derivative Work" of another software received under a "Compatible Licence", you may (in some cases, this is your sole option) distribute it under the compatible licence. All the following conditions are necessary:
- As a whole, your program is a "larger work" combining the software received under the EUPL with another software
- The larger work is a derivative of the other software
- The other software was covered by a "compatible licence".
The notion of "Derivative work" is depending of the applicable copyright law. Modifying the source code (for example, inserting new functionalities, changing the way software operates, localising etc.) will normally be considered as producing a derivative. Simply linking components (without changing functionalities or operation) or aggregating it without changing their source code, will normally not be considered as creating a derivative (in such case each component can be licensed separately).
The notion of "Compatible licence" is depending on the annex of the EUPL. The list includes: GPLv2, GPLv3*, AGPLv3* OSL v2.1 & V3, CPL v1.0, EPL v1.0, CeCILL, MPL*, LGPL*, LiLiQ*.
(* explicitely listed in EUPL v1.2).