This app was mentioned in 10 comments, with an average of 1.30 upvotes
Not sure where to look for now as mine is also nowhere to be found, even if granted access to storage. Here is a temporary solution:
Download and install Docs To Go, then open your downloaded PDFs from Android notification with that app. After opening, tap on the hamburger button, then tap File > Save As, choose the save location and file name (if desired), then tap Save.
I use docs to go. The google suggestion works too but ilI have never been fond of the associated apps.
https://play.google.com/store/apps/details?id=com.dataviz.docstogo