pdftk. You can extract metadata using the
dump_data command and save the output to a text file. Then you can edit/modify the metadata and put them back using the
update_info command, e.g.
Code:
$ pdftk file.pdf dump_data output metadata.txt
$ vi metadata # or edit by means of your preferred editor
$ pdftk file.pdf update_info metadata.txt output updated_file.pdf # check the newly created PDF and...
$ mv updated_file.pdf file.pdf
