How to make InDesign warn you about overwriting a PDF that is open?

Where are the files stored? There's been issues in the historically with some non-Mac file servers and NAS interfering with this behaviour (i.e. they don't give the same feedback to ID that the file is open). That being said, I am not experiencing the same issue here, whether I save the PDF locally or on a NAS. What version of OS are you on?

At my last job, whenever I tried to export from InDesign to overwrite a PDF, it would warn me if that PDF was already open so I could go and close it and then overwrite the file. 

With my new set up, I noticed that I am able to export and "overwrite" PDFs that are currently open, but then when I go to open the PDF, it's still the old verison without changes. 

Ideally, I'd like a warning if I already have the PDF open so I can avoid this.

By @Katie364111881f96

Interesting... First, I don't remember InDesign ever warning me about overwriting a PDF (or any other file) specifically because the file is open. InDesign does warn me, as it always did, about overwriting an existing PDF file (regardless if it's open or not).

If I'm overwriting an existing PDF file that's open, the changes made in InDesign are written in the PDF. That is, if I close the PDF file (obviously, without saving if any changed are made there), then reopen it, then it's the new version written from InDesign.

Or are you describing a different scenario? 

I've noticed this before too - and it's purely a Mac thing reading an old cache or something like that. It's super annoying thing with Macs.
I often move a folder out of the WIP folder into Complete folder - but then saving a file I can see the old folder in the WIP (I only have 1 folder in my WIP at all times and move to complete when done). 

But the folder is not there. It's just not - even though the OS tells me it is. 

I haven't looked into too much - but I think it's a Finder cache issue other than anything else. 

My solution to this
reboot the Mac often.