How to edit pdf metadata from command line?

I need a command line tool for editing metadata of pdf-files.

I'm using a Aiptek MyNote Premium tablet for writing my notes and minutes on this device, import them later and convert them to pdf automatically with a simple script using inkscape and ghostscript.

Is there any command line tool to add some categories to the pdf's metadata, so i can find the pdf later (e.g. with gnome-do) by categories?

Update: I tried the solution with pdftk and it works, but it seems that gnome-do doesn't take care of pdf-metadata. Is there a way to get gnome-do to do that?

Give exiftool a try, it is available from the package libimage-exiftool-perl in the repositories.

As an example, If you have a pdf file called drawing.pdf and you want to update its metadata, Use the utility, exiftool, in this way:

exiftool -Title="This is the Title" -Author="Happy Man" -Subject="PDF Metadata" drawing.pdf

For some reason the Subject entered ends up in the keywords field of the metadata in the pdf file. not a problem in some cases, even desirable, however, this may be problematic, evince and the nautilus metadata previewer do not show this but Adobe Acrobat viewer and PDF-XChange viewer does.

The program will create a backup of the original file if you do not use the; -overwrite_original switch, this means a duplicate will exist in the folder where the updated pdf is. From example above; a file named ; drawing.pdf_original will be created.

use the overwrite switch at your own risk, my suggestion is not to use it and script something to move this file to a better location just in case.

You can edit metadata by using pdftk. Check out update_info (or update_info_utf8 if you need accented characters) parameter. As for data file, below is an example:

InfoKey: Title
InfoValue: Mt-Djing: multitouch DJ table
InfoKey: Subject
InfoValue: Dissertation for Master degree
InfoKey: Keywords
InfoValue: DJing, NUI, multitouch, user-centered design
InfoKey: Author
InfoValue: Pedro Lopes

(Source)

Using Ghostview

Install ghostscript with:

$ sudo apt install ghostscript

Create a file named pdfmarks with similar content:

[ /Title (Document title)
  /Author (Author name)
  /Subject (Subject description)
  /Keywords (comma, separated, keywords)
  /ModDate (D:20061204092842)
  /CreationDate (D:20061204092842)
  /Creator (application name or creator note)
  /Producer (PDF producer name or note)
  /DOCINFO pdfmark

then combine this pdfmarks file with a PDF, PS or EPS input file:

gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf original.pdf pdfmarks

Source: http://milan.kupcevic.net/ghostscript-ps-pdf/

To elaborate on the pdftk method, which is nice because it shows you everything that's being set, at the same time as allowing you to change anything you like, here is a script (for your .bashrc or other aliases file) to do it with one command. This creates a new version of the file you want to edit, opens your favourite editor with the metadatafile, and then implements your changes and sets the file creation/modification time on the modified PDF file to be the same as the original. To use it, after resourcing your .bashrc file, just type

editPDFmetadata myfile.pdf

Here's the alias:

editPDFmetadata() {
OUTPUT="${1}-new.pdf"
METADATA="tmp${1}-report.txt"
pdftk "${1}" dump_data output "$METADATA"
$EDITOR "$METADATA"
pdftk "${1}" update_info "$METADATA"  output "$OUTPUT"
touch -r "${1}" "${OUTPUT}"
}

Simply place the definition above into the .bashrc file in your home folder, then open a new terminal and it will be ready to use.