Update PDF metadata using Emacs?
reddit / emacs

----------------------------------------------------------------------
graduale · 2022-01-31 22:36

I'm trying to find a way of using a `.bib` file to populate the
metadata of PDFs associated with any entry in my `.bib` file. In my
current setup, I have an easy way of getting the path to any PDF
associated with my an entry in my main `.bib` file. If I could modify
the metadata of a PDF, I might be able to then use the information in
the BibTeX entry to update the metadata of the associated PDF.

Is there some way of modifying the metadata of a PDF from within
Emacs? I keep searching online but most results I find are about
attempts to extract information from the metadata in a PDF.

----------------------------------------------------------------------
gjolleyrogers · 2022-02-01 01:33

Cb2bib is an app that does this outside of emacs. There’s source code.
And it works well enough for me.

----------------------------------------------------------------------
graduale · 2022-02-01 02:29

From what I can tell, `c2bib` outputs bibtex entries from metadata.
What I want is the reverse: output metadata for a given file with a
bibtex entry as input. Am I missing something?

----------------------------------------------------------------------
m4xxed_v1 · 2022-02-01 03:33

I use jabref for reference management and it can write metadata from
the bibtex entries in my bib file to the pdfs. I don't know whether it
can do that in bulk, though.

Maybe a starting point?

----------------------------------------------------------------------
art_else · 2022-02-01 10:45

Am looking for a way to edit metadata in pdfs as well, expected pdf-
tools to have this aboard, but unfortunately it doesn't. You could try
the wrapper around `exiftool` on Melpa.

----------------------------------------------------------------------
graduale · 2022-02-01 18:15

Ah I didn’t know there was such a thing. Thanks!

----------------------------------------------------------------------
graduale · 2022-02-01 18:35

Actually I can’t find the wrapper you mentioned. Any chance you can
give me the name?

----------------------------------------------------------------------
art_else · 2022-02-01 20:47

[https://melpa.org/#/exiftool](https://melpa.org/#/exiftool) ;)

I haven't worked with it yet myself, but `exiftool` itself is an
amazing project.

----------------------------------------------------------------------
graduale · 2022-02-01 21:14

Hah. That's what you get from relying on search engines for this.
(DuckDuckGo search for "emacs exiftool", at least, doesn't lead me to
that page!)

Thanks again!

----------------------------------------------------------------------
graduale · 2022-02-01 21:18

Hm, looks like it only works with JPEG files, sadly... I'll see if I
can adapt something from it for my purposes, though.

----------------------------------------------------------------------
oantolin · 2022-02-01 23:39

In addition to exiftool, pdftk can also edit PDF metadata.

----------------------------------------------------------------------
art_else · 2022-02-02 21:29

Please report back when you got something.

----------------------------------------------------------------------
graduale · 2022-02-04 23:48

Nothing too fancy, but it's kind of working so far. There are a few
issues still, especially with passing some markup to `exiftool`, but
I'll put this here in case anyone can do something better with it.
At the moment this relies on `citar`, since it's what I use. I'm
looking to tag this on to a function for moving PDF files to the sole
member of `citar-library-paths`, so that in moving the pdf and
renaming it using the citation key, the metadata gets updated
automatically...

```elisp
(defun my/citar--update-pdf-metadata (key)
  "If KEY has a .pdf file associated with it, update its metadata
information to include author and title values from the entry
associated with KEY."
  (let* ((default-directory (file-truename (car citar-library-paths)))
         (entry (citar--get-entry key))
         (author-metadata
         (cond ((citar-has-a-value '(author) entry)
                (concat "-Author=\"" (citar-get-value "author" entry)
"\""))
               ((citar-has-a-value '(editor) entry)
                (concat "-Author=\"" (citar-get-value "editor" entry)
" (ed.)" "\""))))
         (title-metadata (concat "-Title=\"" (cdr (assoc-string
"title" (citar--get-entry key))) "\"")))
    (if (file-exists-p (concat key ".pdf"))
        (progn
          (copy-file (concat key ".pdf") "citar-library-backup/" 1)
          (shell-command (concat "exiftool "
"-overwrite_original_in_place " author-metadata " " title-metadata " "
key ".pdf")))
      (print (concat "Could not find a file associated with key " key
" in " default-directory))
      )))
```

----------------------------------------------------------------------
art_else · 2022-02-19 23:45

Thanks, will give it a try, but likely will adapt to my needs.

----------------------------------------------------------------------
graduale · 2022-02-20 00:48

Let me know what you come up with!