I use GoodReader to store confidential files on my iPad. GoodReader and iPad makes it easy to take many files to meetings with clients.
GoodReader has the facility to restrict access to itself. But the Files app bypasses the GoodReader restriction when doing browsing. Maybe the same issue happens with other apps.
I cannot find a way of stopping the Files app browsing GoodReader. I am hoping that someone in the TidBits community might have solution to this Files-GoodReader problem.
You need to turn on GoodReader’s encryption option to fix this. There are instructions inside the app’s help. Note that encryption is a paid option for GoodReader (premium feature).