De or het handelingsplan?

The correct Dutch article is:

het handelingsplan

How to use handelingsplan

the handelingsplanhet handelingsplan
this handelingsplandit handelingsplan
that handelingsplandat handelingsplan
our handelingsplanons handelingsplan
your handelingsplanjouw handelingsplan
every handelingsplanelk handelingsplan
which handelingsplan?welk handelingsplan?
a big handelingsplan / the big handelingsplaneen groot handelingsplan, het grote handelingsplan

Dutch words ending in handelingsplan

behandelingsplan

In compound words, the last part decides the article. See the rule