JFileChooser file filtering doesn't actually filter (at least as I intend it to)

Question

I'm trying to set a JFileChooser to only allow choosing a specific file type (pdf) via the showOpenDialog.
I've set a File Filter but I'm confused as to what action on the JFileChooser it has.

What I'm trying to achieve is:

1. Visually exclude other file types to prevent the user from choosing them from the list.
2. Actually prevent selection of other types or an invalid file. (i.e. have the getSelectedFile() to actually return a valid pdf file)

Here is my code:

    JFileChooser fc = new JFileChooser();
    fc.setFileSelectionMode(JFileChooser.FILES_ONLY);
    fc.setAcceptAllFileFilterUsed(false);
    fc.setFileFilter(new FileNameExtensionFilter("PDF Files", "pdf"));
    fc.setDialogTitle("Load MSDS");
    int op = fc.showOpenDialog(this);
    if(op == JFileChooser.APPROVE_OPTION) {
        File f = fc.getSelectedFile();
        lbl_msds_loaded.setForeground(Color.BLACK);
        lbl_msds_loaded.setText(f.getName() + " (Size: " + utils.FileUtils.getFileSizeMegaBytes(f, 3) + ")");
    }

I get this behavior:
Visually - The filtering works and the dialog does only show PDF Files, therefore I can only choose pdf files from the list.
But - I'm still able to manually select an invalid file, by typing in some name in the 'File name:' field and click open (or hit enter).
For example: if I write Untitled.png (which does exist in the currently opened directory) and open, I will get that png file loaded.
Or if write a file name that doesn't exist and click open, I will actually get a new file with that name loaded.
(By loaded I mean the file that getSelectedFile() will return).
Is there a way to not allow the dialog approve the open action if an invalid file is set (based on the filter ofcourse)?
Shouldn't this already be the case when using JFileChooser Dialogs with filters?

What exactly is the filter doing here? The documentation for JFileChooser does not explain any of these aspects.
I would really appreciate an explanation on how this works.
Also what is the difference between setFileFilter and addChoosableFileFilter? They give the exact same behavior.

Finally here's a few screenshots of the Dialog and the JFrame form I'm working on for some context:

https://ibb.co/bFVqVmt
https://ibb.co/5BcsXSW
https://ibb.co/2qq0qr9
https://ibb.co/jMXXXyN
https://ibb.co/g3kvtfd
https://ibb.co/2FshJpt

Thanks alot!