pdf_add_bookmark -- Adds bookmark for current page
Description
int pdf_add_bookmark ( int pdf object, string text [, int parent [, int open]])
Add a nested bookmark under parent, or a new top-level
bookmark if parent = 0. Returns a bookmark descriptor
which may be used as parent for subsequent nested bookmarks.
If open = 1, child bookmarks will be folded out, and invisible if open = 0.