Excel Online doesn’t have a way to insert watermarks—text or pictures you place behind the document text to mark a worksheet’s status like Draft or Confidential.
If you have the Excel desktop application, you can open the workbook, add a simulated watermark, and print your worksheet from Excel. Here’s how:
Click Open in Excel, and follow the instructions in Mimic a watermark in Excel.
If you do this, when you open the worksheet in Excel Online, the image will not be available and you’ll see a message like this:
For news about the latest Excel Online updates, visit the Microsoft Excel blog.