I have a list of files that I need to specify as input to pdftk so it will concatenate them in the order specified. I don't see an input file list as an option in the pdftk man page, but perhaps there's a workaround to achieve a similar result?
This is described in the examples section of the man page:
Join in1.pdf and in2.pdf into a new PDF, out1.pdf:
pdftk in1.pdf in2.pdf cat output out1.pdf
or (using handles):
pdftk A=in1.pdf B=in2.pdf cat A B output out1.pdf
or (using wildcards):
pdftk *.pdf cat output combined.pdf
Of course you can use shell or xargs to expand some list to the input pdf arguments...
Example for concat on all files specified in files.txt (assuming no issues with spaces in filenames etc.)
pdftk $(cat files.txt) cat output out.pdf