Adding page numbers to a multi-page document over existing headers/footers without changing them

I have complied a document from multiple pdf files, each with its own distinctive header and footer that I want to retain.  I want to add page numbers to the entire document, but when I tried that via Headers and Footers, it changes all headers and footers to conform to whatever is on the first page.

The only other option seems to be adding a consecutively numbered text box to each page of the document, which is time consuming (ugh).