It was recently discovered that some characters are disrupted when opening the section editor (editing one section, instead of using the main Edit tab). I have not been able to make this happen any other way. If you have different experience, please attempt to reproduce your issue on the XenForo demo and provide further instructions for me to follow.
As for pasting content from Word, I might expect some characters not working due to it being a different character set (such as the Windows set) from XenForo (UTF-8). The only way to fix that would be to retype any affected characters into the editor, since they get converted at the browser level. Google Docs I'm not sure, since that should be UTF-8. If users are having trouble with specific file contents, you might ask them to supply you a simplified version of the file that, if you can reproduce, you can email to us to review.