hi.
is it possible to create a custom neon iso with more useful apps like office,gparted,k3b?

https://help.ubuntu.com/community/LiveCDCustomization

You can of course build an ISO from scratch, which usually is the better option. live-build or live-wrapper from debian are well suited for that. We use live-build right now. You'll basically want to set a neon repo and make sure to install neon-desktop to get the neon toolchain pulled in. There's lots of documentation online with more indept information.