Can I change an upload URL to match the original upload? I uploaded a PDF in Dupal and used the URL created. Somehow, that document wasn’t saved or was deleted, so now that URL (which is being promoted widely) leads to a page not found. I uploaded a new document, but Drupal renames the URL just slightly.

Can I somehow change this URL to match the original upload or redirect somehow? 
I am not sure which version I use (or where to find this).
There are many ways you can approach this to solve it, but maybe the simplest is to just upload the file with the correct (old) name into the location where Drupal expects it. I don't mean upload through Drupal but through your hosting account into the correct folder. 

Another way is to add a Redirect from the old URI to the new one, through Drupal Redirect module or on the server configuration (.htaccess usually).