ToC=that usually refers to the document content
Bookmarks=that helps you to locate a page and a section of a page. It also stores the desired zoom level set by the person who put the bookmark there
Bookmark != ToC
Sometimes they have the same content but not necessarly
Scribbling=freehand drawing or writing in the document. Does not have any info by itself. It is a layer above the original document. It is not part of the document. not sure if it can be bookmarked.
Comments=text added to the document but it is not part of the structure of the initial document
Highlighted text=text...well...highlighted -here I am not sure how this is stored...
I just checked the structure of a PDF where the scribbles were merged in the doc
Now (after merging) the are stored in the content of the document and they are referred as polyline
There is no bookmark for any of them and this is normal since they are content.
A bookmark is a pointer in the document (by my understanding) and idicates the page and a position on the page (a square) where the content of interest is located