Here are two books that explain the internal structure of Office files. Files with the "x" extension in Office, such as .docx, are actually text files in XML format. However, you won't be able to do anything unless you understand the meaning of the tags. With these two books as a guide, you can create programs that can easily manipulate .docx files. "Introduction to Office Open XML" is truly an introductory book, but it's good for grasping the overview. And "Office Open XML Format Guide" is, among similar books, the most detailed. In other words, with these two books, you should be able to analyze and process the files on your own. "Office Open XML Format Guide" Takayuki Orido I don't remember the purchase price, but I remember it being incredibly expensive. "Introduction to Office Open XML" Yoko Girier / Yoshifumi Takayama / Takashi Morimoto / Akihiko Osuga Price: ¥2000