Worksheets of included libraries cannot be opened.
When zipping the project into an archive using the 'Save as zipped project' option in the 'Save/Zip project as' dialog, included libraries will not be contained in the resulting archive file.
Libraries can only be inserted/deleted if you have logged on with the correct project password ('Project > Change Log On Level' menu item).
In the project tree, right-click the 'Libraries' folder and select 'Insert Library...' from the context menu.
Or:
Select 'Project > Add Library'.
In both cases the 'Insert Library' dialog appears.
Select the desired library and click 'OK'.
The library icon is inserted in the project tree.
In the project tree, left-click the library icon you want to delete.
Press the <DEL> key.
Confirm the deletion in the appearing security message dialog.