Hello. I have long had an issue with PDF downloading when just viewing even in anonymous view and being downloaded to Downloads and changing the date of the folder, which does not seem to behave anonymously. Anyway I used the about config and I am still using this method but that was not enough.
So I changed the default folder for downloads from Downloads to Desktop - now even when PDF downloads in anonymous view and deletes itself it does not change the date of change in my download folder.
Hope it can help somebody else too that has this issue with viewing PDFs and themselves downloading.