A family of Microsoft word processing software products for creating web, email, and print documents.
Sorry, a Table of Contents is created on the fly by a single Word field and editing that manually will break its functionality.
For your scenario, consider using a temporary Master Document to create the Table of Contents, then save result as a PDF. Master documents can assemble a groups of subdocuments for printing or PDF production. Unfortunately, they should never be used long term, as they can easily corrupt the subdocuments. Always use copies of your Word files for the subdocuments. Be sure to delete the master document after PDF creation.
Here's my article about how to safely create a use Master documents, along with a free Word add-in that allows you to automatically create a master and subdocuments from a folder full of Word files: Automated Word Master Documents - Cool Code