Originally Posted by Valkrider
It is currently in M$ Word .doc format and each chapter is a separate file.
My wife handled this recently. She put the chapters into a single .doc file. Word allows you to insert .doc files into your working document. She created a single master file and quickly inserted the chapter files. Each chapter had a heading that received a MS standard style of Heading1, Heading2, etc. When saved as filtered html, it creates <h1>, <h2> tags, etc. When converted from html to EPUB by Calibre, Calibre automatically splits at the chapter headings and built a TOC.