Software that put watermark in background of PDF

Question

I need a software for PDF books that I have on my computer to make me able to:

1. Put my name in the background of each page of my PDF books
2. Put an image of my choice in background
3. Image and writing be misty such that I can read words
4. I can see the watermarks when I print a page

Requirements:

• Free (gratis) software.
• Desktop software, not a webapp. I have both Linux and Windows laptop and computers, so I need a cross platform solution.
• Does not solicit me with popups or ads.

Answer 1

I found a Dysprosium Software Suite here. They call it "Watermark" hence, I edited my post.

It puts photographs and texts with adjustable size and directions in different place.

and one test result

I could use it to convert my pictures to PDF too.

Answer 2

The PDFtk PDF toolkit has, amongst many other features, adding watermarks, there are free and cheap versions both of which offer watermarks, it is cross platform and there is a command line interface so you can add the same watermark to multiple files in a single operation or you can use a batch script to add your standard watermark on demand.

Note that adding watermarks is command line only in the free edition.

I do not work for or on PDFtk.