How can I view hidden files on my Mac? Can’t find a file

MacOS hides some files by default, so there’s a chance your PDF is still there, just hidden.
Try this: open your Downloads folder and press Command + Shift + Period (.) — this will reveal hidden files (they’ll look slightly faded). If your PDF shows up, you can move or open it normally.
You can also try using Spotlight Search by pressing Command + Space and typing the file name to see if it pops up.
Another option is using Finder Search — open Finder, press Command + F, and search for the file name or type (make sure “This Mac” is selected).