Use calibre book converter. You might need a plugin if it’s a super specific drm that needs to be removed (like, say, a library book from the libby app), but calibre will let you pick any output you want and save it as a clean file.

There are some free, open-source command line tools that can do this.

First off, there’s exiftool. It’s the go-to utility to read and write metadata in a wide variety of file types, like mp3, jpg, and you guessed it, pdf. It’s very easy to use:

To read all the metadata in a file: exiftool -a -All <file> (where <file> is the path to your pdf).

To erase all the metadata in a file: exiftool -a -All="" <file> (that’s two double-quotes, to indicate a blank string).

exiftool is likely all you need for your use case, but if you need more advanced PDF manipulation, with a truly dizzying array of options, there’s Ghostscript. Ghostscript can read, write, and convert PDFs, and provides hooks to apply any PostScript commands and options.

To simply print out information on a PDF file: gs -dPDFINFO -dBATCH <file>. This will show you the metadata, such as author, title, etc.

I’m…not going to give you an example of how to use Ghostscript to edit metadata because I’m not confident I’d get it right. The gist is that you use PostScript commands with the -c flag. It is truly arcane but extraordinarily powerful.

If you’re on Linux, you can likely get both of these with your distro’s default package manager. On Mac, use Homebrew or MacPorts. On Windows, you can download prebuilt binaries from their web sites. I think you can even run them on Android using Tmux.