Formatting changes

Hi,

 

I hope someone can help me. I work on MS word and create files that range from 10 to 200 pages. These files have extensive, but simple formatting (mainly the font type and size, tabs, line and paragraph spacing etc). The system (windows 10) updated itself a few days ago and since then it has driven me crazy. Every time I open a file, the formatting has changed. I have to go and change each page. A 9 page file suddenly becomes a 11 page file; the line and paragraph spacing have changed and the pages have spilled over. This happened to the same file about 6 times today. I am afraid of opening the larger files because of this. 

I cannot afford this all the time. I run a training institute and print files as I require them. I have been unable to issue any material to students because of this issue. 

Can someone help me understand the cause of this, and suggest a solution.