Thumbnails for Office documents with nerdy tricks

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Adding thumbnail or preview image for Word, Excel or PowerPoint Office documents is easy, though you won’t find the choice anywhere obvious.  We’ll dig into how thumbnails work for some nerdy extra detail.

Thumbnails are the small images that appear in File Explorer instead of the standard icons for Word, Excel, PowerPoint etc.  Microsoft used to call them preview images.

Saving Thumbnails for all Office documents

You won’t find the ‘Save Thumbnails for all documents’ option anywhere obvious.  It’s not in File | Options where you’d expect it to be.

It’s hiding at File | Info | Properties | Advanced Properties | Summary | Save Thumbnails for all Documents.

Down the bottom of the Summary dialog is the option ‘Save Thumbnails for all Documents’.  In PowerPoint the same option is called ‘Save preview picture’.

Hang on, I hear you cry!  All these settings are document properties, Office says so, not overall settings for Word, Excel or PowerPoint.  You’re right, Advanced Properties is supposed to be settings and info for the current document only.  The ‘Save Thumbnails …’ option is the exception.

Why?  It seems to be a forgotten remnant of much earlier versions of Office. Microsoft has never bothered to move or duplicate this option to Options | Save where it belongs.

Save Thumbnail for single document

To save a thumbnail for a single document, look on Save As dialog (not the ‘Save As’ or ‘Save a copy’ pane) for ‘Save Thumbnail’.

We can’t see how to turn thumbnails on for an existing document without going to Save As.  Please let us know if you can figure it out.

What is saved as the thumbnail?

Office saves the ‘first’ page of each document as the thumbnail

Word: the first page of the document

Excel: the visible/ selected worksheet when saved, using the view/zoom setting at that time.

PowerPoint: the first slide in the deck, the entire slide view.

Under the hood

When a thumbnail is saved, Office takes an image and saves it in the Word, Excel or PowerPoint document.

If you dig inside a modern Office document the thumbnail is at

/docProps/Thumbnail.emf

.EMF is the ‘Windows Metafile’ image format that’s still in use after over two decades.  Windows Paint supports .emf images.

You could tamper with thumbnail.emf inside an Office document, to insert an image which had no connection to the documents real contents.  However, Office would overwrite it with a proper thumbnail the next time the document was saved.

The ‘Save Thumbnail’ setting is held in each Word document within the word/settings.xml file. Look for <w:savePreviewPicture/>

The same setting in Excel and PowerPoint documents is less obvious. Which is a polite way of saying we could not find it!


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