Nick,
A PLA file is a Archicad Archive file. You can save the plan file as a PLA file type. When you do this you will have a choice to include the library parts in the project or alternatively to include all the parts in the loaded libraries whether they have been used in the project or not. This could and usually will create a pretty large archive file so most often you just save the parts that have been used.
There can be problems with this depending of what libraries you are using as this process can miss macros that are called up from parts so you will not have access to them when you open the file.
You should try this out though and see what happens when you open the PLA after saving it. Good way to learn.
Cheers,
Gerald Hoffman
“The simplification of anything is always sensational” GKC
Archicad 4.55 - 27-6000 USA
2019 MacBook Pro-macOS 15.0 (64GB w/ AMD Radeon Pro 5600M GPU)