I work in a small law office.
Increasingly often, we are experiencing the formatting change without permission when we reopen a document. When it does occur, the formatting changes the exact same way. It looks like the style set changes to "word 2003".
We have no idea what is causing this nor have I been able to reproduce it. It just happens and is very frustrating!

Due to this I have learned how to create new quick styles and add them to the styles ribbon on the home page. However, this only allows me to change one line at a time on a 30-40 page document with multiple paragraphs and subsections. This is very tedious and can very easily be goofed. Being that these are legal documents, they need to be correct.
I have also learned how to create a new style set. However, this only instantly changes the quick styles in the styles ribbon on the home page. Also not helpful. None of the style sets (that act more like themes - not the ones in the ribbon on the home page) work to resolve this issue.

Does anyone know why this is occurring, how to stop it, or how to change it back easily?

Please Help!!
-- Frustrated Admin