Use VBA to insert cross references by looping through entire document from insertion point to end

[macropod]

If you save a document as a PDF and use the 'Create bookmarks using Headings' option, the bookmarks pop-out in Adobe Reader functions as an expandable Table of Contents.

Anything fancier would require you to bookmark both the Table of Contents and every Heading in the document, so your save-as could use the 'Create bookmarks using bookmarks' option.

As for your "Click to Return to Table of Contents" requirement, all you need do is create the cross-reference once, then copy that to the clipboard and use Find/Replace to replace all the other instances with the clipboard contents. No code required.