How to add watermark to the doxygen generated pdf file?

@cali_green 

To add a watermark to a Doxygen-generated PDF file, you can follow these steps:

1. Create a watermark image: First, create an image that you want to use as a watermark. This image could be a logo, text, or any other graphic that you want to overlay on the PDF file.
2. Add the watermark to the PDF file: You can add the watermark image to the PDF file using a tool like Adobe Acrobat or a PDF editing software. Open the PDF file in the software and locate the option to add a watermark. Choose the watermark image you created in step 1 and customize its appearance and position on the PDF file.
3. Save the PDF file: Once you have added the watermark to the PDF file, save the changes and ensure that the watermark appears correctly on the document.
4. Regenerate the PDF file using Doxygen: If you want to add the watermark to a PDF file generated by Doxygen, you will need to regenerate the PDF file after adding the watermark. Run the Doxygen command to generate the PDF file again, and the watermark should now appear on the document.

By following these steps, you can easily add a watermark to a Doxygen-generated PDF file to personalize it or protect its content.