When creating Word documents, it is common to add images to make things more interesting. If these images are resized within Word, then that could be adding to your file size.
Word includes the full size image when you resize one in the program,
so even if the image ends up looking small it can be a huge file.
Thanks, Word!
Resizing the image to approximate size before
inserting it to Word helps fix that. There are lots of online image
editing tools that you can use to do this, see this list for some ideas.