pdfmerge4unix has been written in 2003 by Didier F.B Casse. In 2010 it seemed pretty discontinued, so Dominic Hopf resumed this work to fix some issues reported to the Fedora package of pdfmerge in the meanwhile.
The usage of this small but nice tool is pretty easy. Have all your files in one directory, change to that directory and run something like
pdfmerge file1.pdf file2.pdf... fileN.pdf outfile.pdf
You can even mention PDF files in subdirectories like this:
pdfmerge subdir1/file1.pdf subdir2/file2.pdf outfile.pdf
And last but not least you can access a directory from a higher level:
pdfmerge file1.pdf ../file2.pdf outfile.pdf
The current version of pdfmerge is 1.0.5. You can obtain here:
https://github.com/dmaphy/pdfmerge/archive/1.0.5.tar.gz
Checksums can be found at
http://dmaphy.github.com/pdfmerge/md5sums
http://dmaphy.github.com/pdfmerge/sha1sums
If you have any bugreports, improvements, suggestions or anything else you can report those at
https://github.com/dmaphy/pdfmerge/issues