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I didn't know about the eso-pic package. Also, the idea of importing pdfs as a picture is good. And I guess for printing on both sides of the paper, page can be specified in the includegraphics command.

\documentclass[a4paper, landscape]{article}
\usepackage[margin=0pt]{geometry}
\usepackage ...

I am not an expert in Tex, and I can't think of any way that each half will have both header and footer of their own. There is minipage but that is generally used once the body of the document starts, and also demands that the content is manually written for each minipage.

If the solution of the ...

Most of the times only one type of paper is available with the one who prints stuff when you give him your money. And that is A4. Maybe in developed countries people have the luxury of choosing between many sizes of paper, but that is not the case everywhere.

Many documents occupy only one page of a paper and need to be replicated and distributed. Example might be tutorial sheets in universities. So often the back side of the paper gets wasted.

A solution for this might be to cram tutorials for two students in a single paper. Suppose tutorial one ...