I suspect you're seeing this behaviour because the PC on which the document was created has been set up to use Complex Scripts, such as Arabic and/or Chinese. I note that the 'Reveal Formatting' pane (which you can activate via the Style Inspector) reveals that both of these are enabled. Word allows extra space between the lines to accommodate Complex Scripts, regardless of whether the characters requiring them are present in the text.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]