Add object number in sequence while editing a pdf

I have a pdf with 300 pages, and each page was two infographics. I'd like to add a text, say "Item - 1" and "Item - 2" in page 1, and auto increment the same in the following pages.

So in,  page-1, I will have `Item - 1`, `Item - 2`

page-2, I will have `Item -3`, `Item -4`, and so on...

Below is an example image of how the pdf page looks like -

I messed around using Headers and Watermarks, nothing works.

How can I acheive this?