Merge / convert multiple PDF files into one PDF [closed]

How could I merge / convert multiple PDF files into one large PDF file?

I tried the following, but the content of the target file was not as expected:

convert file1.pdf file2.pdf merged.pdf

I need a very simple/basic command line (CLI) solution. Best would be if I could pipe the output of the merge / convert straight into pdf2ps ( as originally attempted in my previously asked question here: Linux piping ( convert -> pdf2ps -> lp) ).

Considering that pdfunite is part of poppler it has a higher chance to be installed, usage is also simpler than pdftk:

pdfunite in-1.pdf in-2.pdf in-n.pdf out.pdf

Just make sure you remember to provide out.pdf, or else it will overwrite the last file in your command

Try the good ghostscript:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=merged.pdf mine1.pdf mine2.pdf

or even this way for an improved version for low resolution PDFs (thanks to Adriano for pointing this out):

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress -sOutputFile=merged.pdf mine1.pdf mine2.pdf

In both cases the ouput resolution is much higher and better than this way using convert:

convert -density 300x300 -quality 100 mine1.pdf mine2.pdf merged.pdf

In this way you wouldn't need to install anything else, just work with what you already have installed in your system (at least both come by default in my box).

UPDATE: first of all thanks for all your nice comments!! just a tip that may work for you guys, after googleing, I found a superb trick to shrink the size of PDFs, I reduced with it one PDF of 300 MB to just 15 MB with an acceptable resolution! and all of this with the good ghostscript, here it is:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -dNOPAUSE -dQUIET -dBATCH -dDetectDuplicateImages -dCompressFonts=true -r150 -sOutputFile=output.pdf input.pdf

cheers!!

I'm sorry, I managed to find the answer myself using google and a bit of luck : )

For those interested;

I installed the pdftk (pdf toolkit) on our debian server, and using the following command I achieved desired output:

pdftk file1.pdf file2.pdf cat output output.pdf

OR

gs -q -sPAPERSIZE=letter -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=output.pdf file1.pdf file2.pdf file3.pdf ...

This in turn can be piped directly into pdf2ps.

This is the easiest solution if you have multiple files and do not want to type in the names one by one:

qpdf --empty --pages *.pdf -- out.pdf