How to permanently delete SEF URLs
AceSEF will continiously genereate SEF URL if any non-SEF URL is routed to it and that non-SEF URL doesn't exist in AceSEF's URLs list unless you've entered any part of the non-SEF URL to "disable-SEF" variables.
So let's say I don't want to store .pdf URLs. Firstly I'll go to AceSEF=>SEF URLs page and filter pdf URLs:

As you may see, I've listed the .pdf SEF URLs. Now I need to copy the marked part of the "Real URL", in my case format=pdf, then go to AceSEF=>Configuration=>Advanced=>Global disable-SEF variables and paste the copied part:

And finally Purge the .pdf URLs. That's it.

As you may see, I've listed the .pdf SEF URLs. Now I need to copy the marked part of the "Real URL", in my case format=pdf, then go to AceSEF=>Configuration=>Advanced=>Global disable-SEF variables and paste the copied part:

And finally Purge the .pdf URLs. That's it.