Save and edit PDFs from Teams on iPad

Dear Sir or Madam,

my school just got 85 iPads and I am trying to figure out how to work with them. When students download PDF files from Safari, they can download those files to their own "school"-folder and open and edit them with the apple PDF app. So far so good. But this doesn't work with PDF files in MS Teams.

When students get PDF files in Teams, they can open, but not edit. They need to download the file first.

Problem 1

When they click <save to files>, they can not choose their own "school" -folder but only app-related folders like Word or Pages.

Problem 2

There is no folder with the Apple PDF app, so I see no way to download the PDF file from Teams and open it in the Apple PDF app.

Can anyone help, please? Thanks in advance

Marc