HowTo: The Correct Way to Copy and Paste Text from MS Word
Whenever you’re copying and pasting text from MS Word, you should avoid pasting it directly into the WordPress WYSIWYG editor. Rather you should use the “Paste from Word” button to remove the extra HTML that MS Word adds to your text. Watch this screencast to see a demonstration.
[...] CSS styling. This usually happens when you copy and paste from a word processor without using the “Paste from Word” button in the WordPress Visual editor [...]