A .yatate file is one project in a single file: a small header followed by a zip of the project folder (scripts, JSON and layout files, fonts, images and PDFs). presets.json can be left out when saving. Generated PDFs are never included.

Open File unpacks it into a temporary working copy, and Save writes it back to the same .yatate. Saving with a .zip extension makes a plain zip instead, which the app cannot open again.