The outline element represents the document outline (aka bookmarks). This element will only be present if the -outline switch was used and the PDF file contains an outline.

The outline element contains nested outlineitem children. Each outlineitem element represents one outline item. If that outline item has children, there will be nested outlineitem elements.

<outline> <outlineitem title="Chapter 1"...> <outlineitem title="Section 1.1" .../> <outlineitem title="Section 1.2" ...> <outlineitem title="Subsection 1.2.1" .../> ... </outlineitem> ... </outlineitem> ... </outline>
An outlineitem element represents an outline item:
<outlineitem title="outline item title" targetpage="page number">
The title is the text associated with the outline item. The PDF spec allows outline items with no text – in this (rare) case, there till be no title attribute.

The target page number is the destination when the outline entry is clicked. Outline items which do not link to pages in the PDF file (e.g., links to other PDF files) will not have a targetpage attribute.