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?

Answer 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

Answer 2

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

Answer 3

I'm not sure how you can keep the exact same resolution -- if that is possible with PDF at all...
But using the -density option might help. I just used this to convert some PDFs into PNGs:

convert -density 200x200 in.pdf out.png

Answer 4

I couldn't find any way of joining two pdf files together while keeping the resolution good and the text intact, but I figured out a way to convert it into a high resolution png file.

pdftoppm -f 1 -l 1 -aa yes -aaVector yes -png -r 300 page.pdf > tmp1.png
pdftoppm -f 2 -l 2 -aa yes -aaVector yes -png -r 300 page.pdf > tmp2.png
convert tmp1.png tmp2.png +append -quality 100 page.png

This takes to first two pages of page.pdf and joins them into a side by side high resolution png file.

Changing the last line to

convert tmp1.png tmp2.png +append -quality 100 page.pdf

will result in a pdf document output as I later figured out after messing around with pngtopnm, pnmtops, ps2pdf.

Answer 5

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