How to programmatically add a background to a pdf?

Question

Given a .pdf file (produced by Inkscape with the LaTeX option, but I am more focused on the .pdf), is there a way to add programmatically a background (ideally, the background would be a rounded rectangle) to it? I am thinking typically of a python script or a C(or objective-C) library.

Typically:

I guess I should be easier to act directly (maybe via the command line) within Inkscape, but I am looking for a solution on the .pdf

Answer 1

If your background is also a PDF, you can use cpdf:

cpdf -stamp-under stamp.pdf input.pdf -o out.pdf

Answer 2

Working further from the answer of johnwhitington I found, that qpdf allows for that as well with the "underlay" option:

qpdf --underlay "background.pdf" -- input.pdf output.pdf

Great advantage: qpdf is available in most distributions. And as allways you can look at qpdf --help to find even more options to specify the page or to work inplace i.e. no need to specify an output file.

Ghostscript and Imagemagick allow for the same, but I found it quite hard to have a proper solution and the .pdf will become a rasterized image.