Permanently in Project vs. Temporarily in Project

Projects can contain files that are permanently or temporarily in the project.

Permanent files

Files that are set to be permanently in the project stay part of the project even when you close the file.

Temporary files

Files that are set to be temporarily in the project are removed from the project once you close the file. When you close the project file, these remain in the project just like permanent files do.

When you open a new file, it is considered a temporary file. If you want to keep the file in the project even when you close the project, you must set the file to permanent.