I think there's more going on here than just saving to a flash drive. That's quite OK provided you remove the drive 'safely' afterwards. If you have removed unsafely, though, you may have corrupted it that way; either way the document appears to have acquired some serious corruption.

I suggest you 'repair' the document by inserting a new, empty, paragraph at the very end, copying everything except that new paragraph to a new document based on the same template (headers & footers may need to be copied separately), closing the old document and saving the new one over it. You may still have some cleaning-up to do afterwards, but that is better than losing the lot - which is what you may now be at risk of.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]