Creation of a table of contents from a long PDF

I would appreciate some help with simple word processing. In short, I have a long PDF (317 pages) which as no detailed table of contents. I would like a detailed table of contents.

Document is structured into 8 Units. There are multitude of sections and sub-sections in each unit, all of which are numbered. It would be great to have a single table of contents which lists every section and subsection in order. For example,

Unit 1 - Understanding Governance, Risk and Compliance
1. Introduction
2. Historical Issues
2.1 Scandals
2.2 The global financial crisis
... and so forth

Apologies, the file is too large to attach through the web interface which has a max of 5MB.