What is DOCX?
What Word has saved since 2007: a zip of XML parts, replacing the binary .doc that came before it. It is a page format through and through - paragraphs, styles, revision marks - with no notion of a typed value anywhere in it, so a table in a Word file is text arranged in a grid rather than data.
What is NDJSON?
One JSON object per line, with no wrapping array. That small change is the whole point: a program can read a record at a time instead of parsing gigabytes into memory first, which is why log pipelines, bulk importers and search indexes all speak it.