Reordering large PDF files using command line tools - pdf

Question

I'm working with PDF files that have hundreds of forms within them. Each form is 2 pages long, so in most files pages 1-2 is the first form, pages 3-4 is the second form, and so on.
However, there are several PDF files where the page order of the forms are reversed. In these cases, page 1 is the second page of the first form and page 2 is the first page of the first form, page 3 is the second page of the second form and page 4 is the first page of the second form, and so on.
I want to reorder the page order in these files so that the pages are in this sequence: (2(1), 2(1)-2, 2(2), 2(2)-1, 2(3), 2(3)-1,...,2n,2n-1), where n= total number of pages/2.
I've been looking for a way to do this using command line tools such as cpdf, pdftk, etc., but to no avail. The files are quite large so I would like to do it by using command line tools.
Any advice will be greatly appreciated!

Answer 1

CIB pdf toolbox of CIB (https://www.cib.de) has a (non free) command line tool version, which supports all possibilities of PDF merging in one run.
Did you try poppler-utils?
i think with the command line tools pdfseparate and pdfunite utilities you can achieve all you want.
http://www.manpagez.com/man/1/pdfseparate/
http://www.manpagez.com/man/1/pdfunite/

Answer 2

Would it matter to you if the order of the forms inside the PDF is changed? For example if instead of
form1-reversed,
form2-reversed,
form3-reversed
your resulting file would look like
form3,
form2,
form1
?
In this case you could just run PDFtk so that it completely reverses all the pages of the original file:
pdftk in.pdf cat r1-1 output reversed.pdf
(Prefixing a page number with the letter r references pages in reverse order. That means r1 is the last page...)

Answer 3

In case you are on an operating system which supports shell scripting (like Bash on Linux or macOS), you can achieve the output of your requested page numbers by something like this (assuming that your n==10):
for i in {1..10}; do
echo -n "$(( 2 * ${i} )) ";
echo -n "$(( 2 * ${i} -1 )) ";
done
This will output 2 1 4 3 6 5 8 7 10 9. Now you could use this PDFtk command for re-ordering the pages as you want:
pdftk in.pdf cat $(for i in {1..10};do echo -n "$((2 * ${i})) ";echo -n "$((2*${i}-1 )) ";done) output out.pdf