Applying or removing a custom preview
You may choose to replace an item’s preview image with something different. For example, a PDF document’s thumbnail and preview are generated from the first page in the document, but you may wish to provide a different image.
To apply a different image as a preview, select the item, then right-click the item and choose Apply Custom Preview from the shortcut menu. You can then choose a supported image file for the new preview image.
To regenerate the original preview image, select the item, right-click it and choose Regenerate Thumbnail.