From Floor Plan: File > Close closes the entire Project.
External files (GDL Object windows, pictures) remain open until you close them separately.
Reopen Project Tabs/Windows of Closed Project
When you close a project with many tabs/windows open simultaneously, ARCHICAD will reopen these the next time you open the project.
Re-opening all these tabs/windows may take time, especially if they must be rebuilt.
If the number of tabs/windows to be re-opened exceeds 20 (not including PhotoRendering windows), a warning dialog lets you re-open just the frontmost tab/window (plus the Floor Plan).