Hi Neil,
Welcome to Microsoft Community.
I would like to know if the issue is with only one single document or is it with all other documents.
Meanwhile let us start Word 2010 in the safe mode and check how it works.
To do that, close Word. Click on Start – All Programs – Accessories – Run, and in the open box type in Outlook /safe and hit ok. (Note: There is a space between Outlook and /).
If the application works fine safe mode, try disabling the add ins for the application and check the result,
- Click the File tab.
- Go to Options.
- Click Add-ins.
- Select or clear the options that you want.
I hope the above suggestion helps.
Thank you.