If your document has many headings, it's a good idea to add a table of contents in case it will be accessed outside Google Docs, for instance, if you export it as a PDF or EPUB document. You can even ...

You can create a table of contents in Microsoft Word where every chapter title links to the appropriate chapter. Then you can keep these links live when you convert the document to a PDF.

With Kindle Create, you can apply professional looking formatting like drop caps and chapter headings and automatically create an interactive table of contents.