Concatenate PDFs but extend pdf's to be even number of pages

Question

I want to concatenate a bunch of PDFs but for printing purposes I would prefer that empty pages are added to each document that have an odd number of pages. Can I do this with PDFTK?

Answer 1

Certainly. Just create a blank page with (for example)

echo "" | ps2pdf -sPAPERSIZE=a4 - blank.pdf

and add blank.pdf to every document that has an odd number of pages. E.g.

pdftk \
BLANK=blank.pdf \
A=foo1.pdf \
B=foo2.pdf \
C=foo3.pdf \
cat A BLANK B BLANK C \
output bar.pdf

Answer 2

Here's a simple little script that will iterate over all pdf files in the current directory and concatenate them into a single PDF, using LaTeX. PDFs with an odd number of pages will have an extra blank page added after them:

#!/bin/bash

cat<<EoF > all.tex
\documentclass{article}
\usepackage{pdfpages}
\begin{document}
EoF

## rename the PDFs to something safe
c=0;
for f in *pdf
do
        ## Link the PDF with a safe name
        ln -s "$f" "$c".pdf
        ## Include the PDF in the tex file
        printf '\includepdf[pages=-]{%s.pdf}\n' "$c" >> all.tex;
        ## Get the number of pages
        pages=$(pdfinfo "$c".pdf | grep -oP '^Pages:\s*\K\d+')
        ## Add an empty page if they are odd
        [[ $(expr "$pages" % 2) != 0 ]] && 
            printf '%s\n' "\newpage\null" >> all.tex

        ((c++));
done

printf '\\end{document}' >> all.tex;
pdflatex all.tex

Since this is LaTeX, you can do all sorts of extra stuff. For example, you can have each PDF in its own section, with a clickable table of contents:

#!/bin/bash

cat<<EoF > all.tex
\documentclass{article}
\usepackage{pdfpages}
\usepackage[colorlinks=true,linkcolor=blue,linktoc=page]{hyperref}
\begin{document}
\tableofcontents
\newpage
EoF
## rename the PDFs to something safe
c=0;
for f in *pdf
do
        ## Link the PDF with a safe name
        ln -s "$f" "$c".pdf
        ## Include the PDF in the tex file
        cat<<EoF >> all.tex
\section{${f//.pdf}}
\includepdf[pages=-]{$c.pdf}
EoF
        ## Get the number of pages
        pages=$(pdfinfo "$c".pdf | grep -oP '^Pages:\s*\K\d+')
        ## This time, because each PDF has its own section title
        ## we want to add a blank page to the even numbered ones
        [[ $(expr "$pages" % 2) = 0 ]] && 
            printf '%s\n' "\newpage\null\newpage" >> all.tex

        ((c++));
done

printf '\\end{document}' >> all.tex;
## Need to run it twice to build the ToC
pdflatex all.tex; pdflatex all.tex;

Answer 3

For future wanderers like myself. I wrote a script combining the answer from @Faheem Mitha and the answer here

#!/bin/sh
# USAGE: ./concat-pdf.sh *.pdf output-file.pdf

ALL_FILES=""
BLANK_FILE="/tmp/blank.pdf"

for OUTPUT_FILE; do true; done
if test -f "$OUTPUT_FILE"; then
    echo "$OUTPUT_FILE already exists"
    exit 1
fi

echo "" | ps2pdf -sPAPERSIZE=a4 - $BLANK_FILE
for PDF_FILE; do
    if [ "$PDF_FILE" != "$OUTPUT_FILE" ]; then
        pages=$(strings < "$PDF_FILE" | sed -n 's|.*Count -\{0,1\}\([0-9]\{1,\}\).*|\1|p' | sort -rn | head -n 1)
        ALL_FILES="$ALL_FILES \"$PDF_FILE\""
        [ $((pages%2)) -ne 0 ] && ALL_FILES="$ALL_FILES $BLANK_FILE"
    fi
done

echo "pdftk $ALL_FILES cat output \"$OUTPUT_FILE\""

pdftk $ALL_FILES cat output "$OUTPUT_FILE"

rm -f $BLANK_FILE