There may be varied reasons why you should be required to have a watermark on an Excel spreadsheet. For whatever reason you have, here are some simple steps to follow to achieve what you need. Bear in mind that this is an image, be it a picture or text, that sits underneath the text that is in your spreadsheet. It does also appear on every other sheet in the file. So design your watermark carefully and test it thoroughly, so that you do not have to make changes once you have deployed it to the company.
Create your image
- Use whatever tools you have to create a suitable image as your watermark. I shall be using PowerPoint as I am very used to it, to create both text and picture images.
- Save it as a file that is compatible to use in Excel.
Here is a list.
*.emf
*.wmf
*.jpg
*.jpeg
*.jfif
*.png
*.bmp
*.dib
*.rle
*.gig
*,emz
*.wmz
*.tiff
*.svg
*.ica
*.webp
Here is my text example. 
This is my image example.
Here is an example Excel spreadsheet that I would like to have a watermark in. it is in page layout view so that you can see the effect. 
To add the watermark
- Click where you can see the [Add Header].
Or in normal view
- Select Insert tab and then select the [Header & Footer Tool].
The ribbon changes to be the Header and Footer ribbon. 
Your flashing cursor will be in the header area of the page.
- From the ribbon select the [Picture Tool].
Your are presented with this. 
- Select the Browse button.
- Locate and insert the file you require.
In the Header area of your spreadsheet, you will see this. 
To see what the watermark looks like click anywhere in the spreadsheet.
You will see this. 
If you should need to change the watermark
- Click in the Header area of the page
- Select Picture form the Header & Footer ribbon.
You will be presented with this question. 
- Select Replace.
- Select the new file you require.
- And click in the spreadsheet to see the result.
Making changes to the Watermark
You can tweak the watermark once you have inserted it into your spreadsheet.
- Click in the header area to activate the Header & Footer tab.
- Select the tab.
- Select the [Format Picture Tool].
Here you will have the access to selecting changes to size and the ability to crop the image. 
When using a logo as I have you may like to select the washout feature in the Picture tab of this Format Picture Window. 
Making adjustment on the scales for brightness and or contrast. 
Resulting in this. 
Have fun and don’t forget to test this out with different files to see that you can still read the information that you require before you go live.
One more point. If you use conditional formatting that has solid colour across the row or down a column then your results will possibly be disappointing as conditional formatting sits above the watermark in the payers of the spreadsheet. 
OR
