pdfpages : what does the 'signature' option mean?

Question

My issue

I have an A5 pdf that I want to print in order to make a booklet made of folded A4 sheets:

(source)

---

My trials

I use this code to generate the pdf-to-be-printed-as-is:

\documentclass[a4paper]{article}
\begin{document}
    \includepdf[pages=-, 
            nup=1x2,
            noautoscale,
            signature=16, 
            landscape,
            delta=0 0cm]{myA5pdf}
\end{document}

Bonus: a MWE for an 8 pages A5 document

\documentclass{scrartcl}
        \usepackage[a5paper,twoside]{geometry}
\begin{document}
        \begin{Huge}
        1\clearpage
        2\clearpage
        3\clearpage
        4\clearpage
        5\clearpage
        6\clearpage
        7\clearpage
        8\clearpage
        \end{Huge}
\end{document}

However, I think I do not understand the meaning (and the functioning) of the signature option.

I have read the documentation and this post that say:

signature Creates booklets by rearranging pages into signatures and setting nup=1x2 or nup=2x1, respectively. This option takes one argument specifying the size of the signature, which should be a multiple of 4.

but the meaning is then no clearer for me.

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My questions

So my questions are:

1. What is the meaning of signature?
2. Which argument (multiple of 4) should I chose:
   • when myA5pdf has 4*n pages?
   • when myA5pdf has 4*n+2 pages?

Answer 1

In the context of bookbinding, signature equals (even if technically incorrect) sections, that are not our beloved hierarchical level #1, but rather booklets that are then stitched together to form a book. (source - you can see here a book made of about 50 signatures (i.e. booklets))

In the context of pdfpages, the argument of the option signature refers to the amount of pages of the original pdf you want to have per section (hence a multiple of 4). Here the example of the influence of signature when importing a 16 pages document:

Answer 2

Books are traditionally sown in sections which are then joined. Each group of pages sown together is a single signature. So, if your book has 400 pages and each signature contains 8 pages then the book consists of 50 signatures.

For a booklet or short book, you likely have a single signature. So the number of pages in the signature should be the number of pages in the document plus enough empty pages to bring the number up to a multiple of 4.

Hence, if the booklet has 4n pages, use signature=4n. If the booklet has (4n+2) pages, use signtuare=4(n+1) and 2 additional blank pages will be added to make up the balance.