Never ever open, edit or print from Office files on flash drive. Always copy to and from the flash drive to the hard drive. Flash drives are notoriously unreliable when so used and will corrupt your data if, either you disconnect without closing properly, or there is insufficient room on the drive to accommodate the working files as well as the original file. You may get away with it for a while, but inevitably you will run into the sort of problem you have experienced.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com