What does "Save preview image with this document" mean?

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Hi robleyd, It is a serious question, although I can certainly see how the answer might seem obvious.

I asked because my assumption was that the preview image is the first page of the file and the file already contains it. So why ask if it should be saved? Because that did not quite make sense, I thought perhaps it was referring to something else.

Now I am wondering if the preview image could be a separate image than the first page. Might that be correct? Also, what would be the advantage of saving or not saving it? That is, why does this question need to be asked?

Why not TIAS? Do a little research: open the .odt file as a zip archive and see if there is a directory named Thumbnails in it and look in that directory. Result will depend on the save setting. See what else you can observe about files with and without the thumbnail.