One of the under-used apps on the iPhone, iPad, or iPod Touch is Files. This free app that comes with iOS from Apple allows me to create, scan, store, search, edit, share, and manage my documents, files, and folders. I can use the storage on my device but I can also access Apple iCloud, Google Drive, Microsoft OneDrive, Dropbox, Box, Adobe Creative Cloud, and connect to most file servers.
Learn more here https://support.apple.com/en-us/HT206481
