Standard catalogs are installed under the shared content folder. The default location is:
You can move catalog files to a different folder. You can also change the shared content folder. For more information, see Migrate Specs and Catalogs.
Spec files are installed under the shared content folder and to the default project folder. If you create a project, spec files are copied from the shared content folder to the new project.
By default, spec files are project specific with each project including its own spec files. If you want to share spec files between projects, you can change the spec file folder using AutoCAD Plant 3D toolset Project Setup.
Catalog files are not part of a project.
You can set AutoCAD Plant 3D toolset to check periodically for changes to a spec file. When you add a part to a piping model, the model retains all the information, even if you remove the part from the spec file.