@stpijb

Those .zip are all world files, they can't be used a schematic.

But there are several ways to change it into a schematic file:

1. Load it as a single player world
and use the schematic mod
to save part of the map
into a .schematic file

2. Load the world file into some
other apps like MCEdit, which can
be used to transform a part of the world
into a .schematic file

If you're lazy to do things above, you can go visit https://www.minecraft-schematics.com/

It's where those schematic users upload their projects,
most of them can be download as .schematic

NOTE: Only tag will notify the user, say my name won't. (tag with @<user>)</user>