Filtering documents in the mobile app work like a combination of the dealboard and documents tab that's in the web app. You get a helicopter view of all your documents and can easily take action on the deals that are about to expire.
How to filter documents in the Mobile App
Click on the Folder icon second from the left at the bottom of the app.
Then click on the dropdown list (example on the video "All documents")
Click on the option you would like to see.