For a recent job application, I needed to combine several pdf files into a single one and to number its pages afterwards. I already knew that I would be able to use PDFtk, a smart CLI tool I mentioned in a previous note to combine the pdf files, but I was not sure how to proceed for the page numbering. Turns out that PDFtk is also useful for this too!

To install pdftk on Ubuntu (or Debian) and MacOS, you should look for pdftk-java:

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# ubuntu
apt-get install pdftk-java
# MacOS 
brew install pdftk-java

Once installed, it is relatively easy to find short tutorials that explain how to combine pdf files with PDFtk, for instance, there is a very good one on Make Tech Easier. Basically, it is a simple call to the command cat of PDFtk:

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$ pdftk file1.pdf file2.pdf file3.pdf cat output final.pdf

For the page numbering, I found this post by Dr. Chloé-Agathe Azencott. Following Dr. Azencott did, I created number.tex (see below), an empty document with pages numbered (my final document had 15 pages):

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 \documentclass[12pt,a4paper]{article}
 \usepackage{multido}
 \usepackage[hmargin=.8cm,vmargin=1.5cm,nohead,nofoot]{geometry}
 \begin{document}
 \multido{}{15}{\vphantom{x}\newpage}
 \end{document}

Then I called pdflatex to obtain number.pdf with the desired 15 pages:

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pdflatex test_number.tex -o test_number.pdf

Then I used the multibackground argument of PDFtk concisely introduced in the documentation :

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$ pdftk input.pdf multibackground background.pdf output final.pdf

Finally, I combined these two steps in the following makefile so that I could rebuild my application with make:

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# combine all pdf documents I needed: the
pdfs := $(patsubst %.md, %.pdf, $(wildcard *.md extra.pdf))
target = final.pdf

ALL: $(target)

$(target): $(pdfs)
	pdftk $(sort $(pdfs)) cat output tmp.pdf # sort and combine pdf
	pdftk tmp.pdf multibackground numbers.pdf output $(target) # create final pdf
	rm tmp.pdf # remove the temporary file

# convert Markdown files to pdf files (pattern rule)
%.pdf: %.md
	pandoc $< -o $@

Hope this could be useful!