See post #12. Assuming, like the post you quoted, that a Mac is involved, that is likely to be where the difficulty lays. For example, there is a setting in Safari ("General" pane) to allow "trusted" files to be automatically opened. This may be a source of problems. Similarly, Stuffit Expander on Macs seems to sometimes go awry and decide to go about extracting the contents of Office XML-format files (.docx, etc.), which are really zip archives with another name.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]