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This article discusses the known issue that occurs when you try to pinch to zoom Office Art content.
The pinch to zoom does not work for Office Art objects, you'll have to use the zoom slider.
Steps to reproduce:
Insert some Office Art contend (Like a rectangle).
Leave the shape selected.
Try pinch to zoom and nothing happens.
Note: You will no longer be able to drag the object either.
The zoom slider will work normally.