The Files app, despite looking like a folder to store things in, is a content management app for iPads, it's arrival marked the beginning of the iPad having a new operating system called iPadOS. Files lets you work with folders on the device and with most online cloud based systems; GoogleDrive, OneDrive, Foldr and Dropbox.
The App Files, keeps all your content and work organised, additionally you can scan any document, save it to a folder, then annotate and share it, all from within the app.
This video tutorial is an example of one of the one hundred and fifty videos supporting twenty different self paced courses for enhancing the curriculum with technology.
For more tutorials on working with PDFs and keeping work and content organised on the iPad have a look at our course iPad For Teachers.