( resource psdoc, string text [, int parent [, int open]] )
Adds a bookmark for the current page. Bookmarks usually appear in
PDF-Viewers left of the page in a hierarchical tree. Clicking on a
bookmark will jump to the given page.
The bookmark has no meaning if the document is printed or viewed but it
will be used if the document is converted to pdf by either
Acrobat Distiller™ or Ghostview.
The returned value is a reference for the bookmark. It is only used if
the bookmark shall be used as a parent.
Returns the identifier of the bookmark or zero in case of an error. The
identifier is a positive number.