Excel does not include a true watermark feature, but you can approximate a visible watermark by inserting an image file into a header or footer of a worksheet.
In visible watermarking, the information is typically text or a logo which identifies the owner or marks the media in some way.
Since headers and footers are normally displayed on every page of a workbook, this method of watermarking is an easy way to ensure that a logo or other necessary information is present on all pages.
To find out all the details read this short tutorial on how to Insert a Watermark in Excel.
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