How to edit an iso image and recompress a extracted folder back to a bootable iso?

I have an .iso image of Ubuntu 16.04. I wanted to edit it by adding some more packages so I extracted it, and then when I try to compress it again to .iso image it doesn't boot.

Even though when I extract it and re-compress back to .iso with no edits it still doesn't boot in VirtualBox, USB nor DVD.

How can I make it bootable again ?

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.