De or het subdocument?

The correct Dutch article is:

het subdocument

Rule Words ending in -ment: usually het. See the rule

How to use subdocument

the subdocumenthet subdocument
this subdocumentdit subdocument
that subdocumentdat subdocument
our subdocumentons subdocument
your subdocumentjouw subdocument
every subdocumentelk subdocument
which subdocument?welk subdocument?
a big subdocument / the big subdocumenteen groot subdocument, het grote subdocument