The best way to understand the format is to create a simple one-word document with MSWord and observe how editing the document changes the underlying XML. I’d like to give you enough information on DOCX internals so you don’t have to reference the ECMA specifications, a massive 5,000 page manual. While DOCX is a complex format, you may want to parse it manually for simpler tasks such as indexing, converting to TXT and making other small modifications. This is why most business documents are created in the DOCX format there’s no good alternative to replace it. The PDF format is not a competitor because PDFs can’t be edited and they don’t contain a full document structure, so they can only take limited local changes like watermarks, signatures, and the like.

Its closest competitor - the ODT format - is only supported by Open/LibreOffice and some open source products, making it far from standard. With approximately one billion people using Microsoft Office, the DOCX format is the most popular de facto standard for exchanging document files between offices.