Verifying F-Droid Download Graphene OS mobile device

Hello, I am unable to open the asc and apk files in “Storage/Downloads” in Graphene OS on my mobile device to verify download of F-Droid.
I receive an “unable to open file” message when clicking on one file and a “permission not granted for downloading unknown app” for other.
Has anyone encountered this problem and found a solution?
I understand, maybe mistakenly, that if I trust the downloaded file, I may enable download anyway by applying settings.
Thank you for any time, comments and assistance, and apologies in advance if information needed has been left out.

2 posts were merged into an existing topic: Help needed to verify the f-droid app APK