system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does .docx do that .doc could not?
gpt
docx is a cleaner and more modern format.  It’s compressed, too, so it  ends up being a smaller file.

docx files are actually zip files.  If you change the file extension from .docx to .zip, you can unzip the file and see what is inside.  There are folders in there and xml files which contain the different types of data that can go in there.  Note:  Copy the file first before you unzip it so you don’t break your original file.