How to merge pdf:s using Imagemagick (resolution problem)

Question

When I try to merge two .pdf files using Imagemagick

convert pdf1.pdf pdf2.pdf temp.pdf

the resulting temp.pdf file seems to have very low resolution. How can I keep the resolution same as in the source files?

Solution 1

Barns's right, but if pdftk didn't work try ghostscript.

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=temp.pdf pdf1.pdf pdf2.pdf

Solution 2

If every file you want to merge is in the same folder:

convert -density 150 $(ls -rt *pdf) output.pdf

the argument -density 150 keeps the quality of the merged PDFs.

Solution 3

Imagemagick's convert command is normally used for converting image files from one format to another, and in this case, it is possible that it is actually performing an internal conversion of sorts before outputting the two "images" (PDFs) into a single file.

I would suggest you consider using the PDF Toolkit (pdftk) instead http://www.accesspdf.com/pdftk/

From the examples on the website, this should be as simple as:

pdftk pdf1.pdf pdf2.pdf cat output temp.pdf

Solution 4

I always forget how to do this and find this question first when I search.

convert -density 600 file1.pdf file2.pdf -resize 50% new.pdf

The linked example has the density at 144, however, that has never been high enough to not appear pixelated.

http://web.archive.org/web/20130311071316/http://studio.imagemagick.org/pipermail/magick-users/2009-September/022958.html

Solution 5

If running linux you can also try poppler which provides pdfunite which concatenates without manipulating the resolution.

View more solutions

Comments

[Leopd]

I'm running on OS X 10.6.1 and I tried to install pdftk via Macports. It seems that pdftk is deprecated on Mac, the installation would not finish. So, I tried to do this using Imagemagick.

[Marco]

-1 for suggesting to rasterize a (possible) vector image. That's not the way to go.

[Iguananaut]

On Ubuntu pdftk was no problem to install from apt, and it did the trick gloriously. I've used ImageMagick to stitch together PDFs before with great success, but because it rasterizes PDFs first (understandably--it doesn't work with vectors) it doesn't look so good for most text documents. But pdftk worked great--thanks for the suggestion.

[Josh]

A side note on your all PDF syntax, you can omit the sub-ls command: convert -density 150 *.pdf output.pdf

[Brionius]

Worked perfectly, and speedily too - much faster than using ImageMagick with the -density flag.

[Sablefoste]

Sorry, the link is dead now.

[Jagtesh Chadha]

This should be the correct answer. Not that ImageMagick doesn't work; it works too. But as @Brionius noted, gs is much faster and the quality of the resulting pdf is top notch.

[shantanoo]

'*.pdf' and '$(ls -rt *pdf)' may result in different output.

[Colin D]

Note that you could use *.pdf instead of the list of pdf1.pdf and pdf2.pdf at the end of this command to convert all pdf in a folder to a single pdf.

[lesolorzanov]

I had some problems with the font, some pages lose their font. Is there a way I can choose it?

[Rosamunda]

It's an excellent tool, and here's how to do it: unixblogger.com/how-to-easily-merge-pdf-documents-under-linu‌​x

[Dan Ortega]

Great ... thank you

[Dan Ortega]

Let's upvote this one, pdftk works way better than ghostcript doing this.

[Nathan Chappell]

had to do a snap install, and the quality was very good.

[Paddy Landau]

Please don't ever use ls like that. (1) If some file names have spaces or special characters, the command might fail or, worse, cause data corruption. (2) ls doesn't have a POSIX standard, and is therefore not guaranteed to be portable. (2) You need to quote the results, but you can't do so because of the subprocess. Instead, to find files, use the find command or, better, use the shell as @Josh explained.