How to change a PDF's title? (not file name)
To answer the question you asked, &quot;How do I change the individual PDF title, either in Acrobat Reader or in Finder?&quot;, you can't. Neither Acrobat Reader or Finder, by default and natively, have the capability to edit that information. It needs to be done before being exported/printed to PDF or use an app capable of editing PDF Documents.
The industry standard is Adobe Acrobat however it's an expensive app and overkill if looking to just edit that information.

If you have exiftool installed and want to do it from the command line in Terminal, use the following syntax:
exiftool -Title=&quot;New Title&quot; /path/to/filename.pdf


To clear the Title, just use: -Title=&quot;&quot;
Other meta-data can be changed in a similar fashion.