A free demo version of this tool, which will process only the first 3 (sub-)bookmarks in the file and create a TOC from them, is now available. The full version has unlimited functionality, of course.

Special Offer: Since this tool is closely related to my other tool, Create Bookmarks from Titles, I'm now offering both scripts for a bargain price of just $99 (each one costs $75 on their own). Click here to purchase them both directly via PayPal.

Update: (22/08/2017):
I've improved the way the TOC is generated and included a brand new feature: It is now possible to maintain the style of the bookmarks in the TOC itself. This could be their text color or whether they are bold, italic, or both. The TOC will reflect these features, while still being clickable, just like before.
And this new feature is also available in the free demo version, if you want to test it out before purchasing the tool!

With this script you can generate a fully functional Table of Contents (TOC) for your PDF file, using just the bookmarks structure.
The script will analyze the bookmarks of your file and will add the newly created TOC where you specify, including working links to the pages the bookmarks link to.
It will even add an extra bookmark at the top of the list to itself.

Here's how it looks like in action:

After we click the "Create Bookmarks from TOC" button, the TOC is generated.
We can then save it as a stand-alone file (without links), or embed it into the main file, with clickable links:

After we choose to insert the TOC into the file, it now looks like this (notice the "Contents" text is clickable, and also that the styling of the "Contents" and "Preface" bookmarks has been maintained in the TOC):