Update PDF metadata using Emacs?

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.

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

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?

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?

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.

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

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

[https://melpa.org/#/exiftool](https://melpa.org/#/exiftool) ;) I haven't worked with it yet myself, but `exiftool` itself is an amazing project.

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!

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

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

Please report back when you got something.

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)) ))) ```

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

Let me know what you come up with!