# Merge two pdf files side by side in command line

command lineimagemagickpdfpdftk

I have got two pdf files with same number of pages and want compare each page with the corresponding page in the other file. For this I would like to merge say page 1 of File1.pdf with page 1 of File2.pdf so it gets one page in the new document. Then page 2 of File1.pdf with page 2 of File2.pdf and make it page 2 of the new file.

In this question I learned already that I can put two pages on one page with the --nup option of the pdfjam command:

pdfjam File1.pdf File2.pdf --nup 2x1 --landscape --outfile File1+2.pdf


The same can be achieved with the ImageMagick package:

montage *.pdf merged.pdf


But this puts together page 1 and page 2 of the first file and does the same later on with the second file – not as intended.

What I did is to split the two documents. The first file got even numbers in the file name, the second odd numbers (actually I created the files anew with appropriate file names). Then I merged all files again with

pdftk *.pdf cat output merged.pdf


and finally put two pages on one with

pdfjam --nup 2x1 --landscape --outfile merged2up.pdf merged.pdf


I could write a script with a loop doing this, but I was wondering whether there is an easy one-liner to achieve this? Maybe I didn't find the right pdfjam, pdftk or ImageMagick command?

You can split File1.pdf and File2.pdf into pages and then combine those tmp files into File1+2.pdf like so:

# Split files, note the naming scheme
pdfseparate File1.pdf temp-%04d-file1.pdf
pdfseparate File2.pdf temp-%04d-file2.pdf

# Combine the final pdf
pdfjam temp-*-*.pdf --nup 2x1 --landscape --outfile File1+2.pdf

# Clean up
rm -f temp-*-*.pdf